>>1560049Cross-chaining and narrow chains do have an effect on durability, though 10s+ chains for MTB are made to handle it better.
Thing is that the ring on a 1x is typically specced at the same position as the big ring on a triple, so the top half of the cassette is good to go without extra wear and the bottom half is used much less by most riders*.
You could have it in the middle position and only have an extreme angle in like two cogs on each side, but with some bikes you get the chain fouling on the second smallest cog when you're riding the smallest one and that's pretty much a non-starter.
*Most MTB riding in practice is done in a 2:1ish to 3:1 gear, so about the 15-18 cogs and smaller.
People that use the lower gears a lot are typically one of the following: a) trail riders hopping up rocks or short, steep, muddy sections, b) people that climb a lot, i.e. gravel/tourers and a lot of what casual XC is, or c) those without much experience or fitness that went 1x because of the meme, or because they couldn't grok front shifting or just because that's what the bike they liked had.
a) and c) aren't likely to get much issue with wear because they will be putting more abuse than use on components; people on b) will be better served by multiple chainrings because they may also use the highest gears a lot but also in practice 2x is still very widespread there so I'm assuming that for people with common sense it's not a massive issue, as ideally your cassette spread/chainring size(s)/chainline should be tweaked to suit your most frequently needed ratios.
