Why many texting apps still don't let choose specific parts to copy from a message?

https://lemmy.world/post/2744279

Its super strange, especially since Android originally allowed it. When I get an authentication code sent the notification gives an option to copy it, and some apps just automatically input it if I leave the app open when the message is recived.
I once had a keyboard app that also copied OTPs automatically, could’ve been GBoard, it doesn’t seem like a universal feature since SwiftKey doesn’t have it in my case.