I think this is the first time I disagree with you. Yes, a provider can like a client, it happens, but we have absolutely no right to expect their eye not to wander. Sex can get stale with the same person over and over again and some men are in this hobby for the variety, or maybe even just have that one off fantasy that his regular can't provide (always wanted to sleep with a (insert random type here). It isn't personal, it doesn't mean he doesn't still enjoy his regular provider. It is on the provider to be professional and maintain a clear head.
SP's are human as well. Some like individual clients and are hurt when they become less attentive. As well, there is the loss of professional pride when your client's attention wanders. Imagine if you lost a client from YOUR business. You would feel a little crestfallen and awkward too. Some women are very competitive about how attractive men find them and can be bitchy if they feel that they have been bested.
Some girls are harpies. Some aren't. There are no hard and fast rules with people.