It makes even more sense to hand API keys only in situations where it is in their business interest, and not in situations where it isn't in their business interest. I think giving Microsoft access to YouTube is not in Google's business interest, and it seems they agree.
Maybe they are wrong, and this hurting them. But regardless, it is within their right to run their business in the way they feel is optimal. The only time the government gets involved is in the case of monopoly, and I highly doubt YouTube is a monopoly or it is impossible for Microsoft to make a competing service.
That's an interesting view of what a monopoly is. By the same standard, Google can make their own OS (actually, they do), so it should be right for Microsoft to prevent Chrome from installing on a Windows box, right?