It's simple advertising. People have a higher chance to use a product if it is advertised to them. I don't think there is a microsoft app these days that doesn't have a copilot logo visible in it at all times (even Paint).

That's like asking how installing a default browser helps boost that browsers market share.

Does that answer your question

No, because of course I want to use a browser, so I will download one if there isn't a default.

Not the case for Azure or Office