- Want a KVstore? Do you know autovacuum? Do you know the connections pool limit? Do you want throughput or safety?

- Want a queue? is it sequential? Is it throttled? Is it fanout? Is it split by topic?

- Want a pubsub? do you care about more than once? do you care about losing messages? do you care about replaying messages?

- Want a lock? Do you know the connections pool limit (again)? Do you know about statement_timeout?

Yes, you can solve almost all issues listed above, but it's not that trivial.