Why does Netflix have half a dozen different database/database-esque systems?

Snowflake, Hive, Cassandra, RDS, Druid, Presto

Is there a good reason for this that people without experience at FAANG orgs can't grasp? To the naive, it seems like mixing Postgres, MySQL, Mongo, and Oracle.

Also why is it on Medium under a Paywall, they are worth, quite literally, nearly $200 billion dollars =/

Not sure about all of them but different databases have different use cases. It's not necessarily Postgres vs. MySQL where they are competing databases for the same use case. Snowflake, for example, is a data warehouse that (I believe) stores data in a columnar format. This makes it much better at performing aggregate queries (how many shows were watched on netflix today?) but a lot slower for specific queries (where in this episode is gavinray currently at?).

Huh, even MySQL and postgres are not apples to apples - we are just now launching a service in MySQL instead of our standard postgres because MySQL has features that postgres doesn't (better connection pooling, potential data partitioning)

For others reading your comment though, I did want to list some things I have used with Postgres that relate to connection pooling and data partitioning:

* PGBouncer for connection pooling/sharing.

* Postgres Table Inheritance for table partitioning (https://www.postgresql.org/docs/12/ddl-inherit.html)

* PGPartman for automating the creation of partitions (https://github.com/pgpartman/pg_partman)

* Citus for low-barrier data sharding (it's a Postgres Extension like PostGIS) (https://www.citusdata.com/)