I dont believe its the oil or OCI necessarily, since the 80s or 90s consumers as a whole have been maintaining their cars like garbage. Its engine design and engine design philosophy where emissions/economy are being heavily regulated by gov and desired by consumers, all while having to pump out better performance numbers than previous generations that puts engineers in a pinch. Many in this thread have already stated this in so many ways.
If you look at the root causes of the engine failures of modern engines, its all from trying to get acceptable power numbers and low end torque(as 90% of drivers never go above 4k rpm) from the tiniest lightest least fuel burning engine. This involves thin aluminum engine blocks, direct injection, and sometimes turbochargers. Cooling systems and gasket/seal material is infinitely better than the past, but combustion chamber temps are sky high with everything turbo'ed and/or high compression which is attainable by DI, and the engine blocks, pistons and rods are thin as possible aluminum. Even with the better cooling systems, surface temps inside the combustion chamber are sky high and cook oil, gumming up passages when oil drainage is already exacerbated by complex head/valvetrain design that causes oil to drain less effectively. With the tiny turbo engines, turbos are an expensive vital item that will grenade far quicker your internals if they aren't getting proper lubrication. For companies choosing to go with larger non turbo 4cyl, those need to be 2.2l+ to satisfy the low end torque and power that the average braindead driver needs, for 4cy of that displacement you need balance shafts to run smoothly, yet another complex part that needs to have proper oiling. And so on and so on..
Basically, manufacturers are engineering themselves in circles around the fact that emissions, economy and power have taken precedence over solid reliable fundamental engine design. And honestly most OEM's do a good job of it walking this line as most engines are pretty reliable, but the failures we are seeing in terms of vital internal parts seems to be going up, instead of the head gasket, seal and belt related problems that were so frequent in the past.
Every manufacturer is doing this, but I suspect the brands like Hyundai/Kia, Chevy also use inferior engine materials and less engineering r+d(as well as hyundai/kia being inexperienced with ground up engine design) because the low sticker prices are coming from somewhere, which is why the result for those cars is rod knock and melted pistons vs relatively minor problems like oil consumption you see with Toyota and Honda etc.
Compare this to the 90s, in my opinion the golden age of engines(if you dont care about emissions). Iron blocks, aluminum blocks were thick, small and sporty cars had smaller displacement but higher revving motors, turbo cars had internals that could handle double or triple the HP of stock. If they had that mentality today along with increase in materials tech and engineering, OEM's could design an engine that could go a million miles at 8k intervals. Many Toyotas from the 90s could do that anyway.
