Owning the things you post and having to host them yourself are two different things. The content is yours, the domains is yours, you pay for someone serving it for you. Hosting is not free and maintaining it is always a hassle a lot of savvy people will pay for a service in order to avoid.
Micro.blog seems to be open source, if at some point you don't want to pay any more, you can always get your data out, setup a server or a rpi, and restore your data. Nothing lost other than some quality time with some readmes.
