(Sorry this is so long but you wanted opinions lol).
This is a subject I'm really interested in, because I'm experimenting with the minimum amount of bike and upgraded parts that can handle real trails without falling apart (and I want to emphasize not 8-foot jumps, just normal riding). As Harold has said it's normally because the bike has been abused, it was made for fire roads and slow, careful singletrack riding, and then people either ignorantly or deliberately bomb downhill at 30 mph and/or take big jumps with forks that are 60-80mm. And then the $200-400 bike falls apart, go figure. The same thing happens with production cars that go on a real racetrack. Some amateur can drive a $30K Subaru WRX around the track and have fun, but if a professional driver gets in his car and drives it around the track, the car is guaranteed to fall apart with extreme driving. Cheap bikes and cars are not built for professional-grade riding/driving, period.
You may have seen the video where a downhill racer buys a $179 Huffy bike from Walmart and takes it on a series of 8-foot jumps, and it then slowly falls apart. Look, I could stack 2000 lbs of stuff on a plastic storage bin and then see the plastic crack and get crushed, does that prove anything besides the laws of physics? I don't understand the point of some of these videos. OK, the downhill racer is justifying why his own bike is $5000+, but he shouldn't insinuate that everyone needs his bike to do normal riding. That's the key point to all of this: you buy the bike that can handle what you are actually doing with it. Please correct me if I'm wrong but 60-80mm forks are not supposed to be taking 'real' jumps ever, right??? And if they do should anyone be shocked that the frame cracks or the fork fails? Even a run of the mill 100mm Suntour XCT fork probably shouldn't take anything over 2 feet; I certainly don't take real jumps with that fork, I know better than to do that. I guess some others don't. I don't blame some newcomer buying a cheap bike and breaking it taking jumps. I do blame some professionals for pretending that everyone should ride like they do and therefore everyone should buy what they buy.
There are a ton of off-brand bikes that will fall apart under hard riding, but the title of this thread includes 'name-brand bikes', and mentions small or moderate jumps. First off, most mail order bikes are not the same name-brand bikes as the ones mentioned on this website (Giant, Diamondback, Cannondale, Santa Cruz, Specialized, etc.). Most of the brand-name bikes named here are sold at REI at the lowest level (not Walmart), at an LBS, or directly from the manufacturer.
I'll tell my own (pathetic) story about cheap bikes, and then use Giant as an example of their low-end bikes and components. My first mountain bike, Pacific Mountain Hunter weighed 50 lbs and the rear brake was rim. I somehow broke the front disk caliper so I never did a real downhill ride with the bike (over 10 mph). Believe it or not it lasted over 5 years until the rear hub rusted out, maybe 2000 miles on the bike, 95% on pavement. Original price of $360 = light riding = cheap bike that lasted long.
The 2nd bike was a complete POS. Pacific Rook. Really flimsy rim brakes on both ends, 3x6 twist shifters that broke from their cheap plastic mountings. Seat so firm I didn't even want to sit down, ever. That bike started falling apart in three weeks, not 5 years, est 300 miles total. And no hard riding. $125 bike = light riding = cheap bike that fell apart and was a waste of money (and time on the dirt road).
3rd bike was a Walmart special, $150 Kent RCT 27.5". And yes it did fall apart, no derailleur hanger, eventually the rear derailleur hit the spokes, broke in half, and cracked the bottom of the frame. It had a lot of other problems too, but it DID hold up on real trails for about 5 months or 1000 miles until the derailleur issue, believe it or not. Although it was scary because the cheap disk brakes didn't always stop in time going downhill and I'd have to jump off the bike, hopefully land on a bush. But I rode this bike hard and it held up, as hard as that may be to believe. $150 price = relatively harder riding but no jumps = yes something broke, but I got my money's worth first.
Next bike that I still have, Merax Finiss 26", rear axle (freewheel-based) broke after around 500 miles. I didn't know it was broken (wheel was slightly crooked but worked fine) and kept riding the wheel another 500 miles; the QR skewer was holding it on, that skewer bent but thank God didn't break. Have rode it hard but not in the Winter using it as a street bike. $350 bike = some hard use but no jumps, rear axle, front derailleur, bad disk brakes replaced, est. 1500 miles so far. Again I got my money's worth for what I'm doing, light XC trail stuff, that's the key statement.
Next bike $517 SE Bikes 1.0 Big Mountain 27.5". Finally an entry-level 'real' bike. 1200+ miles and ZERO problems. Replaced the chain/cassette due to wear, that has been the only problem. The rear derailleur was replaced because of problems shifting into the highest gear but that was probably due to the bike falling on the derailleur earlier and breaking something internally, not the bike's fault itself. Again no jumps with any significant air more than 2 feet, run of the mill XC, light/moderate trail riding. Totally worth the money.
Now let's look at Giant as an example. I like some of their lower-end bikes, like the Talon3 for around $700. But they deliberately hide the low end ones on their websites. They put the $2-3K ones up front and you have to do a search function for anything under $1K. They put the bikes under "Recreational" Why? They still have freewheels and rim brakes on some of their bikes, like the Revel 2 for $370, 80 mm fork. If you ask me, at least a bike like the Merax Finiss above has the potential for a hydraulic brake upgrade because it has mechanical disks to begin with. For the Revel 2, you are stuck with rim brakes, because the conversion would cost almost as much as the bike itself. So cheap name brand bikes can have crap components too just like the cheap off-brand bikes. The only debate is whether the Giant frame is better than an off-brand Chinese frame.
