> Isn't a bolt action a lot simpler?

Parts count of a bolt action is a bit smaller, but that's potentially deceptive. I'm pretty sure the tolerances are actually much tighter with a bolt action. If that isn't a problem, yeah, it's down to whatever gun can be cheaply produced in volume. (I'm sympathetic to the idea that a stamped-receiver semiauto might be a good idea as well)

My opinion here is influenced by the way lever-actions gained so much popularity in warfare and the old West even though bolt-actions were an older design.

> And a lot easier to make strong?

I imagine that's a function of metallurgy in either case. The grizzly-killing lever-action .45-70s in existence today are 140-year old designs scaled up with better materials.

Similarly with revolvers; way easier to make a semiauto pistol and depot-level maintain it than even to just fix the timing on a double action revolver.

Very true, and that's a good example for another reason. Bolt actions and revolvers have that nasty property of rotation in the action (in conjunction with close tolerances!) that somehow cosmically invites jamming. A lever action is more of a simple push-pull kind of thing.

Revolvers have hung onto their reputation for superior reliability with some people but there's so much that can go wrong, and so much that's pretty difficult to fix. In contrast you can build a semiauto that can be taken completely apart without any special tools or knowledge.