Also every time cyl fires there a lot of force there. It does push piston into side of cyl, rod into crank. Crank also has some twist in it after each cyl fires. It does push oil out but there oil but not exactly floating but oil takes heat away so bearing don't scuff. That's my point reason why I say this I've been into industry/mining engines that are never shutdown. Biggest reason why bearings/engine last so long are tighter clearances keeping more of combustion gases out of crankcase. Not all blow by from cyl's there's oil vapor/miss from oil being hot and oil being whipped by moving parts.
Why they change engines out depend on who they are talking too. Mileage, what failed, how up keep has been done, they look at many things and owner. I still don't get the why or reason I work at dealership. Why they replace part on this vehicle and not another. Engineers are really good at telling you to throw parts at it too. It's not always us at dealership level doing this. We go through troubleshooting and do things that we have seen go bad still don't fix it so then you get factory involved. Even they can lead you down wrong path. But we also get into fleets they bend over backwards to help them but owner operator not going to happen unless they know someone. Fleet driver ran engine with no coolant but they policy it why because they just bought 200 trucks with there engine. This isn't just Ford, GM, Dodge and etc they all do it