If you're social you're more likely to care about those around you. Vaccines are also important for protecting vulnerable people in the community, so they were doubly motivated that way.
Surely, you aren't going to also argue that the vulnerable people don't care about others? A charitable argument is that people who cannot get the vaccine for a medical reason probably also shouldn't be around a lot of other people during a pandemic.
But with the current absence of evidence we don't actually know why the social answer is different.
