Classic was made because the private server guys showed Blizzard that it could be done relatively easily and the devs showed it could be done relatively cheaply. Blizzard management was clueless about the actual demand for Classic. Otherwise, they would have monetized it. Corporations don’t give away ‘free’ money (unless the government makes them).
The BC remaster is a different story. Now that they know there is demand, Blizzard wants to make sure they squeeze every last cent they can get through optional upgrades and paid services.