IMHO - if they became an image host it would get in the way of the longevity and portability of their notes themselves.

IMHO, they take the "unix" philosophy of "do one thing and do it well, and interoperate with other things". And i wish more tools operated this way.

It is almost perfect for someone who doesn't want to self-host, but you have to use another commercial service

why am I even paying them, with Joplin I can also sync to Dropbox. And I still have to pay them even if I'm self hosting

I think Joplin is more single purpose since it doesn't focus on the server side, and is just a client

On OSX/iOS, if you don't care about markdown/open-source/self-hosting you should just use Apple Notes