Rich Hickey started Datatomic (along with Stuart Halloway & Justin Gehtland). He also created the Clojure programming language and has been on Hacker News numerous times with many popular talks. In fact they all have made famous contributions.

Many businesses use Microsoft SQL Server or Oracle and don't need access to the source. I'm not saying open source isn't nice, but it is absolutely not a requirement for IT infrastructure.

I'd imagine people rely on many cloud services that are in fact, not open source.