The one thing which you are all missing is the fact of new people are always coming to the party. I for example started with Avengers this year, and only wanted a good representation of the main Marvel characters. I certainly wasn't going to buy a figure from 2008 or any of the first ones available. I want the best head sculpt and likeness out there. That inevitably leads to wanting the latest version. (I'm sure there are enough collectors out there that want the latest and sell the old one too).
So take for example Captain America - Civil War. Latest version. Have you seen the prices ? He is by far the best version, but extremely over priced. If another was released I'd get him cause he's at retail at least. Assuming he is a good representation.
Sure the number of figures they sell maybe lower each time, but it certainly makes sense to keep upping their game. We wouldn't have anything to talk about here either
What I meant with Drax was that if they upgrade the body now (and god knows they need to), they have at least 2 movies to sell figures of him to re-coup the costs. I think there would also be a good amount of people who own Vol 1 version that would want to upgrade too, as the upper body is the biggest complaint for Drax.