These answers are excellent, but I want to offer something informal.
There is stuff inside a proton. An electron doesn’t. You may have heard the expression E=mc2. More energy, more mass. Whizzing is a great example of energy. A proton is much larger.
(NOTE: I may have written a lot of things that are incomplete. It’s energy/momentum and a proton isn’t a bag full of marbles. Some binding energy isn’t the same as whizzing. And what about Higgs coupling? There is a risk in simplifying and conveying limited understanding. But there is also danger in complicating the matter to the point that understanding doesn’t even begin.