i'm not sure why that is.. but perception seems to have something to do with it. back in the 70's and 80's brick and mortar stores ragged about them quite frequently because of their no middle man approach. there really wasn't anything wrong with the product.. they were just in competition with brick and mortars.. who didn't like that.. so they bashed them. some still do.
i was looking to add another marshall bottom to my collection and the brick and mortar owner quoted me the price and said he'd sell me an old x-60 b head for one hundred dollars if i bought the marshall cab. i said "deal". honestly.. it's got a really decent sounding clean channel. the od channel doesn't have quite enough gain for hair metal.. but hey.. they make pedals for that.
i've also got a pre-wired pickguard with ap 11's in my mim strat. i wanted something on the vintage sounding side and i haven't been disappointed by the ap 11's. better sounding than the stock strat pups for sure.