Warranties are mostly to ensure you don't get sold a brick instead of a phone. Extended warranties are better termed service contracts or product insurance. The prices are high, but that might be because it's self-selecting to the people who break products frequently.

I'm not sure how you expect "how long a device lasts" to be defined. Manufacturers do typically design with some lifetime in mind, but it's not clear that has any real world relevance. If I buy a phone and stick it in a drawer it's going to last for a lot longer than its designed lifetime, but if I hook it up to a TV and play Fortnite all day it'll probably last significantly less due to the heat.

As far as software updates, although Apple does 3-5 years for iOS, Google has gone from 2 years to only 3 years, and other Android devices still seem to be in the 1-2 year range. So every Android phone is supported for significantly less than the "4-5 years" you seem to expect.

And the reason the repair bills are getting such interest is because the authorized manufacturer repair shops are so screwed up. They don't do any component-level repair, because the training and equipment is expensive, so the choices are just replace, replace, replace.

tl;dr Mandating a 5-year warranty is just handing out free phones everyone