You also state...
> I would rather set up a matrix server at a lowendbox vps
...and my guess here is that you're going to spend roughly $2-5/month doing this anyway. Plus your hours invested. This is squarely why I'm willing to donate to Signal via my contribution. There's value in someone making sure that this works for me and those I communicate with on Signal. I manage and control far too many other things - so I'm also with you on having that control, knowing about alternatives and controlling my data when and where it makes sense. But I don't want to be in the business of owning a messaging platform for friends and family and Signal fills that gap in a great way.
My post was purely a positional statement and not meant to be construed as any sort of guilt trip of those who don't contribute.