That is one of my main frustrations with Apple: In order to compel more people to use their platform, they made a proprietary communication service, and preloaded it on all of their devices. Now I have to deal with this arbitrary segregation, just because some corporation decided it would help their bottom line.
This is exactly the kind of practice rms warned us about decades ago, and there is nothing any individual can do about it.
If Skype didn't suck so much it could be the cross platform standard.
Apple tries very hard to convince its users that its practices are not the problem, but those who choose not to use Apple products. Anything that doesn't come preinstalled is seen as an unnecessary inconvenience by most iPhone users.
WhatsApp doesn't seem to have this issue, for instance.
Unfortunately, many iOS users do, and Apple cultivates that attitude as its culture.
I've never downloaded WhatsApp, mainly because I don't know anyone who's on it. That's a bigger barrier than anything being preinstalled.
I had apple products as well as others, I chose the rest of the family anyways :p
To me, this is one of the greatest shortcomings of video chat. We went from a universal phone system to a mostly universal SMS system (most private networks still supported SMS) to a segregated video chat system, and it hurts relationships if you're not careful.