Cats have scent glands in their cheeks and paws that release pheremones - when they rub their cheeks or often when they sharpen their claws. Both of these scent glands and their pheremones are "friendly" scent markers - as opposed to territory markers. Territory markers are urine spraying or boundaries are often marked by feces (especially in un-neutered males and unspayed females).
Just like cats LOVE to scratch & stretch - stimulating pheremone release from their paws - they LOVE rub their cheeks on things or have their cheeks rubbed or brushed.
It's such a powerful and universal thing among cats that there is a product based on this principal - it's called Feliway. It mimics the pheremone released by cats' cheeks. They sell it as a plug-in for rooms - like an air freshener, only people can't smell it.
It also comes in a spray. But it helps provide a calmer atmosphere in multi-cat homes; it discourages inappropriate urination in "wrong" places for stressed cats without a medical problem, and for kitties learning where it is OK to scratch and not to scratch, it helps discourage what we consider to be "inappropriate" scratching (but it only helps if they have plenty of appropriate places TO scratch).
We didn't know why all our kitties seemed to love to have their cheeks scratched either when we adopted our first.
....and remember, the only "dumb" question is the question unasked.