Because it’s nearly impossible to convince friends and family to use anything other than iMessage or “the text app” on their phone. The process you’ve described is basically akin to swimming the English Channel for the general public. I’d do it. But expecting anyone else to is just a pipe dream.
I’m already a social outcast and second class citizen for not using imessage. Asking my friends and family to install a whole separate app just to communicate with me puts me firmly in weirdo territory.
Where in the FUCK are you hanging out online that you’re at risk of accidentally seeing one of those kinds of videos? Maybe you need to stop hanging out in those kinds of places.