I noticed months ago, after a friend had bought ESO and been given Morrowind as a free bonus, that it would cost more for me to buy Morrowind for my existing account than to buy the game again. I assumed this would be fixed and was just an oversight by whoever is in charge of prices. Months later there have been no changes to the price in the crown store. Morrowind remains to be £10 more expensive in the crown store than when buying a new copy of the game on steam. Even now when crowns are on deal the value of buying crowns to get Morrowind still greatly exceeds the price of the base game by £6. Not to mention the game is also on deal which only further increases the amount of money you are wasting if you are to buy Morrowind with crowns.
I understand that the value of the base game will depreciate in the eyes of consumers and so deals will be made, such as including Morrowind in a purchase of the base game. However, there should be no reason for the value of the game to be seen so low as to make buying Morrowind with the base game cheaper than Morrowind its self.
I also understand that buying Morrowind on an existing account gives you the privilege of having high level characters that are able to more easily complete quests, bosses and trials that are dotted about Vvardenfell. If it were not for the fact that ZOS need to make money (either through purchases of Morrowind or access to the DLC through membership), this would be the only good reason I can see that Morrowind should not be free for existing players but free for new players.
It is not reasonable to request that existing users be granted Morrowind for free, but it is far more than reasonable to expect that existing players should not have to pay more for a game that they already own.