I always have wondered, why do Korean k-pop fans seem to use gifs more frequently

I think due to a combination of factors.

Gifs are self contained and often "no fuss". In that they are small "videos" one can easily share and post on practically any platform with no fuss. This was especially advantageous in the period prior to the more modern internet ecosystem that easily accommodates short video hosting sites and video sharing with such ease. I think that culture of gif creation became ingrained during the early internet period with kpop communities.

You could quickly pop in a gif with no fuss to share your kpop moment, favorite idol, etc. All in a neat little "can post anywhere and always works" sort of fashion. This is particular conducive to the common practice making memes of ones favorite kpop moments.

Then you add to this their utility in "aesthetics" in that people use them for badges and profile uses....

It just kind of stuck.

The introduction of HTML5 videos like GFYCAT offers kinda blurred the line somewhat later, in that they offer much the same ease of use for short form shareable content in a video package.

But even they still offer the gif option.

All in all, It's a combination of the historical culture adoption along with the ease of shareability of short form content.

I just realized your talking about "Korean" kpop fans. I thought you were asking about just kpop fans in general.