That is not true: you are NOT "buying a license to a game", you're buying the game.
Sorry it is true and wishful thinking doesn't change it. Virtually all commercial software is covered by a EULA - end user licence agreement. You are buying a licence to use the software under the terms described by the EULA. If you run afoul of the terms then your right to use the software may be void or other penalties may apply.
In this particular case I suspect UPlay, Origin, Steam are reasoning that the licence is non transferrable, and since it WAS transferred from one person to another it has become void. That sucks but it's well known that they do this and if you want to avoid it, don't buy licences off some reseller.