It makes sense to me that body shapes were all over the map in the Cambrian. Life had just begun to fit into ecological niches. It was the wild west! A life form only had to have some small advantage to explode onto the scene. Even more so when the niche was empty, so competition was slight.

Niches themselves gyrated wildly as life forms evolved, each being an opportunity for some other life form to capitalize on. Rock, paper, scissors, Spock and on and on!

It took a long time to settle, and for life to start 2nd and 3rd-order optimizations to their niche. It became harder to 'move about' in the evolutionary landscape, when spaces started filling up. Certain body types became 'popular' and took over from some of the stranger ones. It became important not to have too many 'sports' e.g. body details that were expensive and not too useful.

I imagine the Cambrian as a sort of 'initial condition' game of chance for life on Earth. Change things a little back then, and we might have tentacles or pincer mouths!