But how do you know something was taken away in order to add this to subscriptions?
So it isn't about taking away unique potential assets. Because your suggestion is still locking the assets behind subscriptions. Of course you are locked in for 6 months even if they don't put out content. Don't buy the six months and just pay $25 for it separately if you really want the mount. Content droughts are really not much of an issue. Because Blizzard has rarely released major content with in six months of each other.They could make a system where you get a token every 6 months of sub time and you can hit up a vendor to buy something you want, but doing it this way ensures you stay subbed even if they have a content drought. You're locked in for 6 months even if the put out literally no content. It's exploitative behavior, taking advantage of FOMO, all for greed's sake, not to reward players.
So there has always been a period of time with no new content. Yet now it is bad just because they give a $25 mount for free for using the cheapest subscription block. It isn't about greed. It is literally rewarding players, who likely would be playing anyways, to stay subscribed. It has nothing to do with fear of missing out because you literally can't miss out. You can get the mount separately for $25.
You are also over looking how you don't need to purchase a new subscription. As people already on one will be getting the mount as well. It all depends how you have been paying. I bought 6 months in November. I get the mount. Win Win. I enjoy playing a game and get something for free.