I actually would love an answer for this. Especially in regards to the Oly style belt with the taper. I mean, it seems weird they'd ever bother with the back width, but if someone can give me a date when that style of belt was being used, I have an inkling why it may have come to exist...
That said, they can't be that new. Using thick belts to assist in the continental style of bringing a weight from floor to chest was common before the first Olympic Weightlifting competition.