I do choose hotels in part based on free wi-fi. It is somewhat ridiculous that the $50 red roof inn gives free wi-fi, but the $300 JW Marriott or Animal Kingdom Lodge does not. Usually, the nicer hotels charge more and give you something better. With wi-fi, not the case.
That said, it's just a business decision. While I choose hotels based on availability of free wi-fi, not enough people do, and so hotels can make a choice to charge or not. Obviously, the cheaper hotels almost universally think they'll lose business if they charge for wi-fi, while more expensive ones have more of a mixed view. It isn't unlike those infernal bag charges the airlines all charge now. If we all stopped flying airlines that charged for bags, they'd have to change, but we don't.