There's a few clients for Signal, nobody is preventing developers from creating apps; there's Molly, gurk-rs, Axolotl, Flare, signal-cli, Pidgin (with the Signal plugin.
The problem is 3rd party clients don't implement all features because it takes a lot of work and they're created/developed by volunteers - just take a look at Matrix and how many clients support all features or even just group end-to-end encryption (E2EE). Last I checked many third party Matrix clients didn't support encrypted group messages, primarily just Element, the reference client built by the matrix developers. So you have the same problem on Signal that you have on Matrix.
A few things to keep in mind:
Considering the two points above, it's not irrational to come to state the following:
Given the two statements above, assuming both projects need to balance resource constraints, it's safe to conclude, :
It was closed because they use Github for bug reports, not feature requests [4]. The dev even pointed them to the right place. That said, I do agree it would be great if there was some progress made on this front for Signal, but realize its a huge effort and may be best avoided for now as the iOS client still needs some "catching up" to do, compared to the Android version.
Agreed.
Telegram collects all your data by default in a way that's accessible to anyone with enough privileges to their infrastructure.
[0] https://core.telegram.org/reproducible-builds#step-6-comparing-the-appstore-build-and-the-version-built-in-the
[1] https://signal.org/blog/private-contact-discovery/
[2] https://github.com/signalapp/Signal-Android/tree/main/reproducible-builds
[3] https://github.com/ali-fareed/darwin-containers/commits/main/
[4] https://github.com/signalapp/Signal-iOS/issues/641#issuecomment-1276308990