They download apps for all kinds of bullshit because all their friends and people they follow are on there. They won’t install a messaging app if none of the people they interact with are there. It’s not specific to messaging. I was able to convince my immediate family to move to Signal just for our family group chats. It’s not much but it’s a start.
I use eufy as well. The only issue they recently had was that thumbnails were stored in their cloud if you chose to enable them on notifications. If you just select the text option, none of the footage is stored online and everything is local.