Same goes for people who you convince to install Signal. They’ll end up never using it because they just forget about it and they’re not the ones who wanted to use it anyway. Being able to message people on WhatsApp through Signal would also make it a lot more easy to convince people to install it.

As far as I know they already lose money selling them because they make way more money through PS plus and the PS store

That’s what I’m doing. I have selfhosted E-Mail with YunoHost and send it through SMTP2Go.