While I'm on it... this is simple, as the title says.
School enforce uniforms to the point only the school issued swimsuits are allowed in the pool. Funding is tight (as always) and the swimsuits are bought from the lowest bidder.
I don't think they're outright prank items (yes, there's such, or at least once was), rather just low quality somehow. Or maybe purposefully malicious, can't rule that out. The loss of color is over a dozen uses/washouts or two, but they gradually become as transparent as colored pantyhose, and eventually perhaps lose even that remains of color becoming completely transparent. Yet, retain nominal functional in sense of breast support, performance and such, as far it matters. It's also somehow still formally recognized as clothing, so "appropriate" in contrary to them being indeed outright nude.
Girls are rather distraught at first, some at least, for having to swim next to nude. But the school administrators are uncaring and/or unresponsive.
The problem is recognized and escalated early, when it's still rather mild, but isn't acted on, and even the updates of it becoming really bad doesn't seem to reach decision makers, not in any timely manner anyhow. There could be several layered reasons for such, including, but not limited to, the embarrassing nature of the problem.
Meanwhile, everyone is adapting and getting used to this new fashion. While girls are visually nude in the pool, formally they are dressed, there's no obvious problems because
of that and thus no reason for any action and additional spending. The faulty swimsuits will be replaced eventually, on schedule. Next year?
Well, before then the decision may be that spending on swimsuits can be cut to zero, since it won't make much difference to officially recognize the nudity already established in the pool as the new norm, right?
Absurd? Maybe, but not necessarily in the logic of any sufficiently established deep bureaucracy. Ah, the little fact of nudity being embarrassing somehow... that's an entirely social construct that can and may change, and following out such change is likely the point here, even if it's done mostly for silly titillation.