Down in the reddit comments it says it is not self-hosted because of limited "engineering bandwidth".
Also, self-hosted consumer products are hard to sustain profitably. Avenues for monetization are low.
Given that our long term target audience is people like my parents, we did not see enough value in investing in a self-hosted variant, and wanted to reduce the number of distractions.
This is not to say that we are against the idea of a self-hosted variant, just that it is not a priority for us right now.
Also the phrase "ente has an open architecture and source code that has been peer reviewed" that can be found on their website follows a dark pattern: hey, look we are open but not really.