Swift is tightly bound to the Apple ecosystem (even though it can run outside of it), both in tooling, the ecosystem, and developer's perceptions.
These things all feed into each other.
If you're in the (vast, vast) majority of Swift developers then you're writing apps for iOS, MacOS, etc. This means outside of that context Swift goes from being a relatively popular language with a strong ecosystem to an incredibly niche one.
One angle where this could gain traction is devs writing a server side backend for their Apple app - but this use case is sliced apart in practice.
- Teams that start off wanting to use the same language for the app and the backend are likely to pick React Native or similar.
- The larger teams that want/need to write their app natively likely have devs that write the apps and devs that write the server code - so the desire the for language to be the same is lower.
- The pool of developers you could hire that have backend experience and swift experience is much much smaller than either of those two factors alone.
On a pure 'is this language good enough for the problem' level - sure, swift could do the job.
But that's also true of almost every other language.
These things all feed into each other.
If you're in the (vast, vast) majority of Swift developers then you're writing apps for iOS, MacOS, etc. This means outside of that context Swift goes from being a relatively popular language with a strong ecosystem to an incredibly niche one.
One angle where this could gain traction is devs writing a server side backend for their Apple app - but this use case is sliced apart in practice.
- Teams that start off wanting to use the same language for the app and the backend are likely to pick React Native or similar.
- The larger teams that want/need to write their app natively likely have devs that write the apps and devs that write the server code - so the desire the for language to be the same is lower.
- The pool of developers you could hire that have backend experience and swift experience is much much smaller than either of those two factors alone.
On a pure 'is this language good enough for the problem' level - sure, swift could do the job.
But that's also true of almost every other language.