I think it's the "way higher quality battery". There are a lot of very low-quality non-OEM batteries, I've rarely had those last more than 6 months and they were wildly unsatisfactory even then. I managed to source a NOS OEM thinkpad battery off ebay and that was significantly higher quality than the usual junk but still, I think Apple is picky about batteries.
While on the whole I'm not overly fond of the non-serviceable battery model on laptops, I do believe Apple when they say they lose money on their repair service as a whole. I just had my iphone 8+ battery replaced after 4 years (yeah it was starting to get real bad lol), I made a point of having it done at the apple store knowing that 4-year-old glue might not want to let loose, it ended up having a different problem and they ended up replacing the whole phone with a refurb, for the $49 cost of the battery repair. Sold, absolutely came out ahead on that, was starting to get glitchy anyway and it was a refurb phone in the first place, honestly was crossing my fingers they'd break it anyway.
If you have an expensive MBP I think it'd be a hard sell to not take applecare, if you end up needing even 1 display replaced you come out ahead. That's the model, Apple really wants you on Applecare and they lose money doing it, it's all part of the package deal of ownership (which of course is not offered to secondhand owners, that's where they make the money).
It's more of a mixed bag on the cheaper models... display replacement still has a decent service charge plus the applecare fee and it's not all that worth it on a say $700 laptop. You're gonna have paid a total of like $500 anyway if you need to use it, at some point the laptop is just totaled and you get a new one. Also probably not worth it on desktops (with the possible exception of imac). But on a $3000 macbook pro? Yeah I'd do it there for sure.