[scholia]

> Why did IBM even go to Redmond, WA in the first place?

That's not a mystery: it went to license Microsoft Basic, which was the most widely recognized Basic of its day. It dated back to the MITS Altair.

So IBM would have gone to Redmond regardless of Mary Gates.

However, it probably helped with the DOS deal, whereby Microsoft offered to save IBM's operating system bacon. Basic was a known quantity but MS-DOS didn't even exist.