Well, in markets where there's only space for 1, 2, or 3 companies to succeed, then it makes sense to be rewarded for quick growth, so that you can end up in one of the 1-3 "winning" slots instead of going out of business.
The incentive isn't something artificial, it's just how certain markets work. E.g. a city might be able to support hundreds of pizzerias, but only 2-3 ride hailing companies.
Well, nine women can't deliver a baby in one month, but nine women can definitely drive nine riders where they need to go at the same time.
The mythical man-month is about how adding individual new members to an existing software team doesn't necessarily make the team deliver faster (and can even slow them down). Nowhere does it claim that adding more parallel projects or growth initiatives to a company slows the company down.
The incentive isn't something artificial, it's just how certain markets work. E.g. a city might be able to support hundreds of pizzerias, but only 2-3 ride hailing companies.