Why do Seo Taiji & Boys get a pass for being active for 4 years?

they were really influential

Their albums sold really well

That was 4 big and legendary years maybe

It was what they did in those 4 years. Plus there wasn't any competition like there is now. Kpop as we know it wasn't really a thing until they came along.

They started it all, they will always be remembered. H.O.T released music only 5 years (96-01) and last year wasn't that much

I guess at that time, their type of music is far from known/maybe unknown in SK. After they make that sound popular, it blends in with society.