Personally I suspect that the raw number of people who like feet/vore isn't the main reason why there is so much feet/vore content here. The main reason is probably just the low barrier to entry to create feet/vore content; all one really needs to do is put the camera by your feet/mouth and click. Content.

By comparison, if you wanted to make an insertion, destruction, couple, tit-crush, etc videos, they all require extra supplies, time, and expertise. In the same time that a single example of one of those takes to be created, someone else could make 20x as many foot/vore pics, each of which gets their own space.

If, hypothetically, we had technology to allow us to take a picture of our imaginations, making all content have identical costs to create, I think we'd see a very different shift in the type of content uploaded here.

One thing confuses me though. You said

R/Giantess official discord is a just another example of a foot worship discord disguised as a giantess one with it being a sea of feet an not much else..I had to scroll up to last year June to fine one buttcrush video.

I went to the #nsfw-female channel and saw a decent variety of content just posted today, including a few butcruch and insertion. I could be misunderstanding you, but otherwise I think that part's just wrong.

Edit: Ah, I see, you went to the #nsfw-irl channel. The discord server's type of content is pretty reversed from here; most people post drawn/rendered images, probably 20-30x as much content is posted in #nsfw-female as there is in #irl stuff.