You don't need a reason to want to block adverts.
It doesn't have to be for security reasons (although there are good security reasons).
You don't have to do it because you want to lessen online surveillance (although that's a good thing too).
You can do it just because you don't want someone trying to sell you something the whole damn time, getting up in your face and interrupting your reading/viewing.
You can block ads because it's simply a form of self-care.