Well, first, I'd guess that bars with some up and back sweep sell better than completely flat bars, which seem to be virtually nonexistent. And that is probably the result of providing riders with some choice to indulge their personal preference. And, as you point out, you can mostly eliminate it.
I suppose all of your bars are OEM, which probably means they were chosen to be adaptable to rider preference.
I don't find the position uncomfortable and it seems like it might be advantageous to have the outside of your hand bearing on the handlebar for pushing it down in turns, but I haven't experimented with it. I see a couple of articles discussing bars that say the kind of average 4-6 degree upsweep produced a "neutral wrist position," without citing any ergonomic reference. It really isn't much.
But, ultimately, you do you. Most people seem to like some upsweep and if you have a zero upsweep bar there's nothing you can do to gain sweep so there's less ability to "customize."