Now, this is a bit of hockus pokus crystal ball nonsense but I'm starting to have a theory that could make some sense...
I noticed that most of the films we see disappearing are either high sensitivity emulsions or high silver content ones. High sensitivity films are more susceptible to environmental degradation. Also, they need the use of special sensitizing dyes. I'm thinking that the more sensitive the film, the more expensive the dyes (though I have absolutely no idea what they use in those dyes). So, you combine those things together and it ends-up that high sensitivity films get pulled off the lineup.
It could also be that sourcing the chemicals to make the dyes is becoming more and more expensive...