Trailer composer here.
It is certainly true that the amount of composers wanting to break into the industry has increased a lot in the last two years or so. I hear this from libraries who have even more people reaching out to them to get an "in" than they did 2 years ago. Word has got round that this is a career to make money with, so we might be approaching the apex of the "
pork cycle".
The same is also true for the amount of trailer libraries popping up. I can't actually keep up with it, and a music supervisor friend and myself have a good head-scratch about this every time we talk (and compare notes on which ones we notice that popped up and which ones have gone to the wall - this happens as well). It is also true that trailer houses, the ones that actually cut the trailers don't have gold-plated futures either, some suddenly do a lot less well than they used to, for whatever reasons, and the same goes for some composers, too. So like any industry it is in flux, but I can't help but get the feeling that a certain level of saturation has set in on several fronts.
In a way I feel the industry has an analogous fate to that of the sample library world, where in the last year in particular we seem to have reached a nadir, where we have gone from a scenario ten years or so ago where you had to pay an arm a and a leg for EWQLSO, to now being bombarded with new brass and other libraries every other month, and the most ridiculous reductions on sample libraries (even by libraries who said they wouldn't do reductions) being common place now. Similar situation: word has spread that you can make money with developing sample libraries, but the pot is only so big and if more people are sharing that pot more people with be earning, but less money per library, with a few at the top being ok.
So that doesn't mean that people should give up on their dream/hope/wish of being a trailer composer, it just means it is harder than it was 5 years, and even harder than when the industry was in its infancy, when big bucks could be made quickly (form what I heard, I wasn't there for the very beginning).
There is a whole other aspect to this on what one can charge these days and where that is heading, the impact of netflix, amazon prime et al and AI, but that's for a different discussion.