What do you do about sites where the users don't particularly likely said providers? Not everyone uses Facebook or Google or Twitter after all, and a lot more

What do you do about sites where the users don't particularly likely said providers? Not everyone uses Facebook or Google or Twitter after all, and a lot more would rather use an anonymous disposable account than one tied to an existing identity. There's also the fact said systems seem to be a nice target for spammers. They're popular, so they're often attacked. And because they're often attacked, their anti spam defences don't usually last very long. So any spammer now has a nice way to get an account on near enough any site they like, while with a standalone system, they'd at least have to tailor their attacks to the site in question. There's also the fact it silos much of the internet (or at least user information) within the systems of a few large providers, which gives a significant amount of control to said providers.