You’re asking them to do work and open up their chat platform to other devices that are outside of their ecosystem and they have no os level control over. The security aspect of this in itself makes this not something “incredibly basic and easy”.
On top of that, there’s literally no benefit for them to do it. There are plenty of third party options for chat out there, and again, clamoring for them to do this work and maintain a product while still maintaining security for no return is entitled and unrealistic.
People making this argument show themselves to be naive to how software development and business in general works.