My theory is, often companies have a limit for room prices for their employees, but WiFi fees count additional other expenses so they won't matter for the selection of the hotel.
So as a business traveler you don't care to be charged 20$/day for WiFi, your employer will pay for it. Hotels make nice extra money. Only "normal" guests who care, will be annoyed.
In medium tier Hotels and especially Hostels all around the world I never experienced any WiFi restrictions.