It comes preinstalled, works, is free. Why would I look for a different messaging app? What does WhatsApp do that the preinstalled, free, messaging app doesn't?
SMS doesn't do group chats; I think you're thinking of MMS. I agree that it's not a great experience, though.
> Group messages to anyone regardless of platform.
That's the thing though; that's not true. WhatsApp might be available on both Android and iOS, but it only works if the person you want to talk to has it installed and has set up an account. That requires coordination. If I meet someone new and want to get in touch with them, I'm going to ask for their phone number (or email address). I'm not going to ask them which messaging apps they have installed so we can figure out which one(s) we have in common.
Sure, if later on I want to start a long-running group chat including this person, I'll absolutely go to the effort of finding a common chat platform that is not MMS, because MMS is terrible. But if I'm only doing 1-on-1 conversations, or just short one-off group chats, I won't bother.
(Interestingly, for some people, even though I have group chats with them on an alternate platform, I'll still message them 1-on-1 using SMS. Not sure why that's the case, and it's not universal. I guess it's just whatever we'd gotten used to, and saw no need to change.)
I think this is region specific. In the UK and a lot of western Europe, you'd probably assume that the other person does have Whatsapp installed and just try messaging on that. If that didn't work, then you might try Messenger or SMS.
A lot of people I know use groupme for groupchats, especially because they support a lot of users, but then its texts for everything else because its simpler. Chat apps have shortcomings, especially if you live where data connections are spotty which is everywhere in America with a large indoor space. My grocery store might as well be a faraday cage for anything demanding my 4g connection, but SMS goes through instantly.
