Someone comes along with a patch or idea. Bunch of big Postgres people come knock it and it dies right there.
Happened to me when I suggested a more multi-tenant approach back around 2010 and today we have Citus. I was told that (paraphrased) no users were asking for that sort of thing.
I see it kind of happening with the Foreign Key Array patch that the author asked for help to rebase and no one bothered to reply.
Someone suggested replacing the Postmaster with a threaded approach so it could scale better (and showed benchmarks of their implementation handling more connections). Community response was there were already 3rd party connection pools that do the job. An outsider looking in considers this nuts - most people would not run additional components if they did not need to!
Another example: NAMEDATALEN restricts every identifier to 63 bytes - a limit that causes frequent issues (more so now that we have partitioning) and also a problem for multi-lingual table names. It’s been proposed to increase this limit a few times. Every time the answer has been: abbreviate your table names or recompile your own version of Postgres.
Could name a few other examples too I’ve noticed over the years and just sighed at. I don’t expect every idea to be accepted or even welcomed - but there is that sense of bias against change.