As Barry says, covenants are often put in place by the developers of housing estates and, in such cases, they're the only people who can enforce them.
I live on a large Barratt Homes development, built in the 1980s. Every house has a covenant which says that there must be no external TV aerials but just about every house has one. Similarly, every house has a covenant that says the front garden must be largely laid to lawn, whereas the reality is that most have been paved over to create additional parking spaces. (There's even a covenant on my house which says that I'm responsible for mowing a small area of lawn that's in a neighbouring road! I don't!).
Barratt Homes clearly have no interest in enforcing any of the covenants, so everyone here simply ignores them.