I think the problem is it's too risky to utilise a "new" database today that isn't available as a managed option on many platforms.
Neon is just Postgres for the most part -- sure if they shut down it'd be a pain to migrate but you'd mostly be fine just swapping to AWS RDS/Aurora or the plethora of other Postgres providers.
Buying into things like Gel or now defunct RethinkDB mean if the primary company went under you're stuck with a dead DB engine and potentially no managed hosting options.
