"i want to know why is it okay to make hyunjin's songs his arts about the other members but when we make it about felix everyone is flipping???"

In the case of non a/kgae shippers, I've seen this happen a lot in fandoms. It's almost like a weird sort of resource guarding for lack of a better way to phrase it. Since hynlx is the most popular ship for both hyn and flx, people who ship other things consider it greedy for the "big pairing" to get too much of the "proof". It's actually way more complicated (and simultaneously stupid) than I can fit into this anon ask box lol.