There is a stigma in the PC gamer community against Microsoft, especially after Games for Windows. "Steam or go home" sentiments also aren't all that uncommon. As for the accounts - I really don't know anyone who actually uses the MS store (whereas pretty much everyone who plays video games has a Steam account), and I interact with plenty of end-users daily. Maybe it just happens that the area I live in never adopted it, but I would still say that Steam is the better platform to try to get exposure on.