Yes by non-profits. What VC backed python runtimes are you referring to?

Both deno and bun felt like experiments in VC funded language runtimes and both of them failed. It reinforced the idea to me that you cannot productize runtimes and they need to be funded by other means

You mentioned self hosting but if you want something without any lock in, there’s https://prose.sh/ — it open source, supports images, markdown, and you bring your own editor.