I think the university gets a lot of hate as while it is technically a part of the "Golden Triangle," students from the other universities within the triangle i.e. UCL/ LSE/ Imperial see it as being relatively more unserious & having a higher offer rate (i.e. 39.3% for KCL compared to 36.2% UCL, 36% Imperial, 12.2%) therefore less prestigious.
It is still a great uni.
Just stereotyped to be the worst of the golden triangle london unis.