Let's be frank. Gates was from the WASP elites, old money stuff. IBM would probably find a reason to give him the deal rather than to Gary no matter what.
Gates had a version of DOS ready in 6 weeks, while DR was still planning DOS. MS got things going much faster.
I wrote a book report on a biography of Bill Gates when I was 7 or 8. It contained a youthful anecdote about his mother calling him on the house's intercom and him replying after several ignored attempts that "[he was] busy thinking. Maybe [she] should try it sometime!"
An intercom? In a house? So that your mother didn't have to repeatedly yell up the stairs to your brother that food is on the table? Sure sounded like rich person stuff to me.
In particular, his mother – Mary Maxwell Gates – was on the United Way board along with IBM’s chairman John Opel and reportedly discussed her son’s company with Opel a few weeks before they made the decision to license MS-DOS.
https://www.nytimes.com/1994/06/11/obituaries/mary-gates-64-...