The problem is that a black suit is not versatile. There are virtually zero situations, except for funerals, where a charcoal or navy suit will not look better...
Drink the kool aid much?? You think, black, as a colour is "inferior" to charcoal or navy? Please. The reasons are cultural and barely enter the realm of aesthetic considerations for most here, it is born of dogma and imitation of forumnites with superior cultural SFcapital.
Some reasons why you could possibly not want to wear a black suit:
1) Tradition, it is changing but it used not to be done. Keep in mind that someone could do it in a conservative law firm without any problems nowadays or in another bastion of sartorial conservatism so the point is sorta moot in all but the most special of cases. (i.e. you're meeting Prince Charles and don't want to offend his delicate sensibilities because you've got a fetish for big ears and are aiming to score).
2) Doesn't pair well with brown shoes and other IGent accessories. To be honest it's mostly a black suit, shoes, belt + white/pink/grey/pale coloured dress shirt/pocket square. Black as a colour is about as easy to associate than navy, considered not all shades of navy go with all shades of brown and various dress shirts. You might have a little bit more colour choices though.
3) Nothing else, you hardly look like a waiter wearing a black suit or a security guards wearing navy jackets and grey slacks.