Just a nerd who migrated from kbin(dot)social.
Holistically it’s UX.
If my wife or others in my life who use Apple want to contact me, they don’t have to go into a specific app and hope that I’m looking at it. They can go into iMessage, click the camera, and poof, a video call starts up. The only software I use that does that otherwise is Discord, and that’s not integrated with SMS/MMS. It’s the connection too (which is just as much part of UX) - I’ve had problems with Zoom or others due to connection strength, but not with FaceTime.
The fact that it’s a “just-works” solution is important.
As someone whose only apple devices are ipads, the big lockin isn’t imessage vs an SMS client. It’s FaceTime vs, Zoom/GMeet/Jitsi. Mind you, it is nice being able to use iMessage with my wife when I have internet, and then swap over to SMS quickly. Sure, my two devices don’t have a persistent conversation, but her device does.
These are just opinions, but here are the two I know about (I don’t use WhatsApp)
Discord: It’s not just you. You would have to get their other connections, all their servers, and all the connections from those servers to switch. Frankly speaking, Revolt isn’t ready for that to happen. You are one person. I’m sorry, but if I have 1 friend vs. all of my servers and friends, I’m not going to make a meaningful change for the one person. And tbh I’m more likely to be the one than the many. What I would suggest is to try and put yourself between the two services, help to build the communities you want to see, then invite people over.
Instagram: Same issue as Discord. The fediverse doesn’t have the variety of content, the wide range of users, or half the stuff to engage with.
I know that a lot of the cheap Android handsets, which we mostly encounter as prepaid, have interchangeable camera bits.