I don't know how many .NET developers do what I do, but I think a lot of us are doing Enterprise development, typically working with huge databases that have been around for decades. My company does a lot of work with DB2 on IBMi servers, replacing old green-screen applications with new WPF and web applications. It's not the big data you're taking about, but it's the old-school version of big data.

There are few ML libraries out there for .NET (.e.g ACCORD), but nothing near what you can get with say Python. I hope things improve.

F# is HUGE.

There are other things like akka.net, orleans, dotnumerics, accord, alglib. Infer.net for graph based models. A lot of others are proprietary.