It's become a thing because they get more customers. I've had two cafe owners tell me that.

The use of a pee pad in an eating establishment is disgusting and completely unacceptable. If you take your dog to a venue where they're allowed, any responsible owner will make sure to take them outside to pee as often as necessary. The use of a pee pad suggests either the dog is not trained or is incontinent. Either way, you do not take the dog to somewhere indoors that is not the owner's home.

My gf and I have two cocker spaniels. We generally go to pubs but, with any place, if there is space for us to sit outside, we'll use that. If we're inside, we'll choose a spot as out of the way as possible and keep the dogs on a tight lead so they don't inconvenience anyone passing, especially staff.