Plenty players recruited by big schools HAVE attended that school’s camp. Just understand the camp is just one of many ways the school evaluates potential players. You certainly get up-close attention at their camp.
As others have mentioned, the Stanford Camp gets players exposed to HA D3 and D1 coaches. Most of the Ivy schools have at least an assistant coach attend—Princeton was also present in 2019. And a kid on my son’s camp team committed to Stanford this past summer. He certainly didn’t blow anyone away at the camp but he certainly was evaluated and that evaluation mattered when they saw him at other events after the 2019 camp.