I hear what you’re saying, and were it a college or professional team I probably would agree, but for high schoolers that’s harder. At that age, their very identity and self-worth are dependent on peer acceptance. Not to mention any shy kids who might have felt powerless to speak up. We also don’t know that they didn’t try; one or some may have tried and been shut down by peer pressure. My guess is one idiot thought it’d be funny, convinced a few more, and pressured the rest. “It’s just a prank bro” or somesuch.
That the coach didn’t put an immediate stop to it is definitely an issue.