Secondly, anything could break at any time: the vps provider, the domain provider, the matrix server, the bridges themselves could go unmaintained or suddenly not be compatible anymore.
It's truly a flaky hack, and in truth you shouldn't need a flaky hack to send a photo to your uncle using whatsapp
1: https://github.com/spantaleev/matrix-docker-ansible-deploy
Connecting matrix to non-open ecosystems is a bit hit-and-miss in that it often requires you to run bridges in special ways and there are sometimes ways it breaks unexpectedly. I expect that to improve if the EU passes its law to force more interoperability.
What exactly is preventing you from buying it, if that's what you care about? It's literally what you want.
And dropbox is just rsync with extra whistles, right?
I don't think that modern messaging apps could be trivialized to just "sending text messages". And even if you in particular don't use all the other features, all the other people who create network effects do.