The point with a self-hosted WordPress install is you have full autonomy over your own website/blog, and nobody can interfere with that.
If you use the SaaS WordPress.com offering, then I'm sure it's not much different of a situation than Substack, other than far more customization.
Edit: additionally, with self-hosted WordPress---it's probably the easiest web application to install on conventional web hosting (LAMP stack) that usually the layperson is able to figure out themself and maintain. And is meant to be widely supported over a broad range of environments or PHP versions, unlike most 'modern' software that's so brittle (and often only deployable via Docker or similar).