Why? Swift has never worried about it, and Dart’s target market is a lot closer to Swift.

Swift has made large backwards-incompatible changes 3 times now.

I've been a mobile dev for many years now. Every team I've been on either largely avoided Swift for the first 3-5 years, or was burned hard due to the constant churn.

It's much more stable these days, but personally I'm still wary of the team's (past?) proclivity to make sweeping incompatible changes.

I feel the same way towards SwiftUI, which seems to have an even more rockier upgrade path than Swift.

How many Swift users consider that a good thing though? Swift is on railroad tracks: you have to upgrade on Apple's schedule or eventually you won't be able push your product to the store. Also, 2 to 3 was a nightmare and the Swift team itself is actually pretty chary about doing anything like that again.

Not being able to run project that's using older Swift version on the latest Xcode is a terrible experience tho.