Or for a more concerning example, GitHub is owned by Microsoft who want to sell cloud services so it stands to reason it would be in their interest to have GitHub Copilot steer developers towards building applications using architectural patterns that lend themselves more to using those cloud services, e.g. service-oriented architecture even when it is against the developer's interests.

This doesn't have to be as blunt as promoting specific libraries or services and it's a bias that could even be introduced "accidentally".

That’s because of statistical likelihood and abundance of web content about React which seems to be kinda default choice. Had to be a looong con if it was an ad.

Are people putting up vast arrays of websites to promote products/politics solely to sway LLM-feeding crawlers yet?

I've seen those content mills since before Covid.