Because I prefer it in functionally every way to Windows. I prefer (when feasible) to use open source and/or FLOSS software. I am vastly more familiar with Linux than I am Windows on a technical level. I generally dislike most things about Windows.
and use Steam
It works, it’s convenient, they have a generally good track record of not screwing over users.
I prefer many of the features of Linux distros, but using a client like Steam defeats the purpose of them.
That is a pretty serious leap in logic. You’re welcome to not like Steam on a technical, moral, and/or philosophical level but at the end of the day it is a single application and saying that using Linux while also using Steam “defeats the purpose of Linux” is ridiculous. Linux is an Operating System, it is meant to assist the user in computing. If the user is using Linux to compute they are fulfilling the exact purpose of Linux, that being an open and free operating system to be used by any who desire it.