The default messaging apps on iPhone is iMessage. It’s locked down and can not communicate with any other messaging app except via SMS. Therefore the other apps have to use it to communicate with iPhone users, who you will never, ever convince to download a third party messaging app
One other thing is that none of the third party messaging apps can even use SMS. iOS is designed so that only Apple can use SMS.
It’s been awhile since I’ve used anything but Magisk but usually you have to set root permissions per app, or you can get Magisk notification to request access.