Why do crf450l’s have a lower weight capacity

I have a 2017 CRF 250l and I am looking to upgrade to a 450. My 2017’s max weight capacity is 327 pounds but the 450 is only 220. I myself weigh about that so it’s even feasible for me to get one. Also, how much faster are they? Is it worth upgrading and why is the weight capacity so low?