Been through this as well. There was one database for relational data, one for logs, one for analytics, one for miscelaneous, one for binaries, one for time-series, one for key-values, one for caches and probably a lot more! Total nightmare.
Nobody fully knew how operations, schemas, indexing or queries in any of them worked. Usually someone had managed to hack something together in a week and then the rest of the team just did minor changes to existing queries. Joining between the databases was also a fun exercise.
I blame it all on docker. It's so easy to just docker-compose run grafana:latest, then dust off your hands and claim you have a database running. Articles from HN on how fancy setup Netflix have also contributes to this, you don't have the same ops capacity to replicate a FAANG stack.
In the end all of it got replaced with only mongodb and firefighting went down to 0. Everybody in the team knew how to do everything, from new queries to migrations and backup-recovery. It's probably worse in every aspect on each task the specialized databases were solving, but it works good enough and often bringing a really good swiss-army-knife is better than having a caravan of specialized machines which each require special expertise.