It's really just trying to be as simple as possible. I was motivated by trying to just do the most simple thing I could come up with after I did not really find the other solutions to be something I wanted to build on.
I'm sure they are great, but I want to leave the window open to having people self host what we are building / enable us to deploy a cellular architecture later and thus I want to stick to a manageable number of services until until I can no longer. Postgres is a known quantity in my stack and the only postgres only solution was DBOS which unfortunately did not look ready for prime time yet when I tried it. That said, I noticed that DBOS is making quite some progress so I'm somewhat confident that it will eventually get there.