Why are amateur weight classes different from the pros?

Because the rest of the world uses metric. https://en.wikipedia.org/wiki/Weight_class_%28boxing%29 Ah thanks.

Just noticed that for the most part amateur weight classes are only a few pounds different from the pros, why not just make them the same? Because the rest of the world uses metric. When the (amateur) International Boxing Association (AIBA) was founded in 1946 to govern amateur boxing, it metricated the weight class limits by rounding them to the nearest kilogram. Subsequent alterations as outlined in the boxing at the Summer Olympics article; these have introduced further discrepancies between amateur and professional class limits and names. The lower weight classes are to be adjusted in September 2010, to establish an absolute minimum weight for adult boxers. https://en.wikipedia.org/wiki/Weight_class_%28boxing%29