Living in Seattle and having worked with numerous companies I'm going to happily contest this: Your statement is simply not true, all the way around.
Was MS never even in the running or could it possibly boil down to the cost issue I touched on or perhaps that founders or early engineers chose a different route due to past personal exposure (and would you feel that the financial barrier of entry is a factor in limiting these engineers to this MS software exposure)?
Would have a bit of incentives from MS like reduced license costs steered those early conversations in a different direction or is it simply that the software they offer isn't up to snuff with your particular use cases?