Microsoft has very little to gain from DDoSing sourcehut as at the end of the day GitHub’s competition is like flies, AND Microsoft has a lot to loose if it was discovered they did it
Companies are made of people. Those whose wealth and wellbeing depend on Github being the monopoly may be interested in destroying the competition before it grows into a concern.
It would be really stupid for Microsoft, the country's richest company, to go after a tiny competitor via extralegal means. Absolutely would make no sense. The liability they would incur would be astronomical