Is it though? Batteries themselves are something like $20-60 (e.g. Pixel 8 battery for $43, ebay listing for <$20). The battery is honestly not that expensive, the expensive part is the labor because taking modern phones apart is a massive pain.
It’s about 80-130 € depending on phone model, and that includes work and the battery. If I could just buy a battery online and replace it myself, the prices should be more reasonable. Apparently one day that will actually happen.
And that’s the point here. The battery itself isn’t the expensive part, it’s the expertise and tools needed to do the swap. If phones are required to have user-serviceable batteries, users can just buy the batteries and service it themselves. Many will still go to phone repair places, but prices should come down there as well since it’ll take them a lot less time and equipment.
Just realized, there’s also another benefit. You could bring multiple batteries to a trip and not worry about charging. You know, the way you have always done with DSLR cameras.