Bike Bag allows keeping rear tire and handle bars attached

I mean, you can fly with a box like that.

Problem is, it takes up much more space that way and you're likely to pay more to transport your bike that way. And that's why most reusable bike transport cases soft or hard are going to have their dimensions trimmed down enough that you'll need to remove the bars. I used a hard case once where I had to pull the fork, too, in order to arrange things just so to use the space inside.

What’s your motivation for not removing the handlebar? It only takes a few minutes and saves a ton of space as mentioned above.

I have an evoc bag with the internal frame. I keep the rear derailleur attached, but have to remove front and rear wheels. Handlebar comes off at the stem. It does take time to reassemble, but it fits my Ibis Ripmo and the bag is about as large I bag as I want to carry around the airport anyway.