Maybe because Signal is a piece of crap. Just a bunch of poorly written desktop and mobile clients tied to questionable backends.

And also because... https://dessalines.github.io/essays/why_not_signal.html

CIA Funding CIA → RFA → OTF → Signal. While this article by Yasha Levine gets into the details, it is no secret that the original funder of Open Whisper Systems (the previous name for signal’s development team), was the Open Technology Fund: itself publicly listed as a subsidiary of Radio Free Asia, a US state-run organization whose main goal (along with the other “Radio Free” incarnations such as Radio Free Europe, or Free Cuba Radio) is regime change for those Asian governments who don’t align with the US’s foreign policy interests.

You can’t recommend Signal over anything when it comes to features and service quality it just can't handle large group chats (hundreds of people) and the cross device sync fails often with a “signal can’t display this message”. Signal’s desktop and mobile clients are simply a pile of react and JavaScript garbage that can never be as fast as the native applications from other apps.