The long oil change intervals seem to be (based on Lake Speed's videos) crap. Yes, some oils can be made with better base that doesn't degrade and maintains its viscosity better/longer.
But what can't be extended is the additive package. Additives gen used up, so over time/miles, the ZDDP, Moly, Calcium, etc... get used up. Those things play an important part in the role of the oil. I think the theory is that most of the time the amounts of those things are greatly reduced in more normal intervals (3000-5000 miles). So a 20k mile interval may be OK from a viscosity point of view, or the gov't point of view, it's not OK from the engine's point of view. I'm sure many/most people are also happy about longer change intervals, because it's cheaper and more convenient. Auto manufacturers are probably also happy about it, because modern engines, in theory, are made with better metalurgy and tolerances, so should be lasting a LONG time compared to older engines, but if the oil isn't protecting the motors as well due to longer change intervals (despite the fact that the oil itself is also much better than oils from 30, 40, 60 years ago) then they are still selling more cars and motors because they are still wearing out.
That's my theory
And many/all of the oil folks are doing it. When I go into a parts store and look at the oil, there must be 5-10 different kinds of Mobil 1. The "Mobil 1 FS" is marketed as a Euro-centric oil. Mobil 1 has a PDF that shows the phosphorous and zddp levels, but not the full additive package
https://www.mobil.com/lubricants/-/media/project/wep/mobil/mobil-row-us-1/files/mobil-1-product-guide-rev-31.pdf
From their website they show 16 different types (my FLAPS just doesn't carry them all in stock)
My guess as to why they don't just sell 1 or even <5 different types, is money. I think the main characteristics could be broken down to base oil quality and additive packages. THere are probably additive packages that are very basic/minimal. There are additive packages that conform to various specifications required by different manufacturers. Then there are other additive packages. I think a lot of the "high mile" oils have seal conditioners, so for many/most of the oils, there could be a second version with the seal conditioners. And all of the different packages and additives add to the cost potentially in varying levels. A lot of oil manufacturers are, IIRC, reducing the Calcium in oils for the newer direct injection cars because it causes detonation or something like that. But I think Calcium is a good detergent for other motors that don't have DI.