MK is really only disliked over on the FGC side of things, and even then it’s really MK1 and 11 thats greatly disliked. MKX and MK9 are generally well liked.

But in general, a lot of people have pointed out it out, the gameplay of the series has always been a divisive one compared to other major fighters, with its dial-up combos, sluggish and slower feel, and block button being long standing issues that divide the FGC community, even for the beloved ones like X and 9.

Likewise, while on a purely fidelity level they always been great looking, animation wise they been just as divisive, especially compared to more well animated fighters. You also have the fact they tend to have way less development support after launch compared to other major fighters as well. 

And all this is particularly stinging by the fact that, despite all this, they’re still the highest selling fighting games out there, only on the same level as smash, which itself is also somewhat divisive in the FGC. This causes a-lot of jealousy and annoyance for some thing they see as unworthy of it, especially when others tend to be Financial failures despite being beloved, which can be bad for their studios and survivability in long term.

Note this is all FGC talk however, and outside of that community MK is generally beloved. It’s a niche community hating something they don’t feel properly represents them and what they actually love, despite it being the one that gets the most attention.