Honestly? Efficiency & battery life without sacrificing speed/performance.
If you need great battery life (or simply don't want to have to worry about charging your laptop frequently), it's hard to swallow ~4-10h battery life of a typical X86 laptop when MBA/MBP are consistently achieving 10-16+ with real-world use.
...not to mention the other perks MacBooks hold over their competitors, e.g. fit/finish, display quality, speakers, etc.
>They serve completely different markets.
Do they, though? With so many things being web-based these days, it's not very hard for most people (without specific needs) to switch to an M1 as their primary device without experiencing problems.