Everyone tends to give this advice of owning your own work through a central location and syndicating everywhere else. In other words, building your own platform.
But generally speaking, sometimes you have to leverage platforms that have the current attention of the world as that is where you will drive engagement to your platform. It is fairly rare to just win organic search traffic especially starting out so you have to "hijack" some attention here and there where applicable.
If you follow any notable person online who writes, creates content, etc, they are not afraid of going where everyone else is going whether that means they may have to be exclusive with their creations for awhile or whether that platform allows them to retain the rights to their creations.
At the end of the day, it all helps them build an audience that they can take anywhere and there's many possibilities depending on what you'd like to do with that platform.
Substack is that popular thing right now because it combines both the content and email list ownership that you can then take anywhere were it to go under tomorrow. It is a very accessible way to "own your work" today, especially for those who don't want to bother setting up a wordpress blog or similar.