Google is a massive organization, and this is probably the LEAST ridiculous example of redundancy! I've lost count of the number of database systems they've developed.
I don't know if they're still as committed to this today, but historically Google has been famous for allowing their engineers to spend some percentage of their time on self-directed side projects. This leads to lots of engineers working on the same sorts of things in different ways.
Some of Google's databases are just more functionality on top of an existing one, though, rather than being created from scratch. Spanner is built on top of BigTable, and F1 is built on top of Spanner, for example.
I don't know if they're still as committed to this today, but historically Google has been famous for allowing their engineers to spend some percentage of their time on self-directed side projects. This leads to lots of engineers working on the same sorts of things in different ways.