There may be a cultural divide here: I mostly work for government funded projects, to the point I have never had to put an ad on one of my projects. Our clients frequently to require using some libraries, some in-house developed, some third-party.

About libraries, I try use them only when the cost-benefit ratio is very clear.

For example, I avoid premade UI component toolkits, because in practice they are a bit of a scam: they are helpful at first, but in the long run they may be a terrible burden.

Pity my main client is starting to enforce one of them (a third party paid one, if you can believe it), as a (probably misguided) way to enforce consistent UX.