You can try but rarely is it successful unless you're a super popular influencer. If Mr. Beast came out with a platform and said use it, he'd get a million users in a day, all of them evangelizing to their friend groups and maybe it would take off. Otherwise you're just going to get ignored unless it's easy enough.
WhatsApp is easy enough and good enough. It is not the best solution, but part of its allure is that it is owned by a big corporation. Governments and billion dollar companies use WhatsApp as their backbone because it is big. They aren't going to roll their own.
And when someone is completely against WhatsApp... Why? If it's because you hate Zuck and Meta, then fine. Personal grudges are fine with me, but not a valid reason to dislike the platform for everyone, just yourself. The data that they get is who you are sending messages to, when, and the overall size. Everything else can be blocked. The content of the messages is secure unless you decrypt and backup elsewhere. One of my WhatsApp numbers is on a number from a VoIP line not even tied to my name or ID in any way. Meta collects information that I am talking to hundreds of delivery drivers arranging my deliveries. I'm ok with that.
They don't have any of my info. I don't have any social media accounts apart from Lemmy and a now retired reddit. Works well enough. And the older people can use it easily enough. Getting my mother to switch to telegram? Isn't happening. But WhatsApp... She's down for that.