The ad market is more competitive and very crowded there is no reason to use Unity for your ads if someone else offers a better deal.
Also Unity did try focusing on increasing ad revenue over the last several years, it didn’t work out that well.
> leaves everybody feeling great about Unity.
Making their engine entirely free would make most people feel even better.
> untapped sources of income to dumber product managers.
Why? Most Unity’s client’s don’t make much if anything at all a few make massive amounts. Due to the fixed licensing model the latter barely pay anything to Unity (e.g. compared to how much they pay storefronts/platform owners/ad networks). If they want to continue growing their revenue Unity has to get more from these customers, there aren’t that many other options.