It's easy enough to do: pack the divot with some snow, smooth it down and put some water on top.
Unfortunately, no rinks really keep a bucket of slush handy, so you either have to scrape up snow with your blade or go in search of a bucket and the zamboni snow pile (usually outside) or the operator who probably cut the ice and went to do some other job during the freestyle. It's time-consuming.
Coaches and skaters don't want to lose valuable ice time patching divots, if it means leaving the ice. So, small divots stay there and we hope the zamboni fills it in. Really big ones get a cone put on top and then we hope the zamboni fills it in unless someone gets it slushed first.
Sky Rink (when it was really in the sky) used to keep a bucket of slush rinkside. Freestyle sessions ended with filling in the divots. I've never seen it anywhere since then, except during competitions.
A few weeks ago, our zamboni malfunctioned and carved two train rail-width ditches into the ice about 4-5' in length.
Three of us spent 20 minutes patching them with slush and hockey pucks. They were so deep, they took off the white ice paint, so now we have these two dark, but level! claw marks on the ice. One of my students asked about it and I said our cartoon shark at center ice got a little frisky, lol.