This was not a Supreme Court "decision." The Supreme Court has not decided to hear the case; they haven't even been asked to hear it. Instead, the plaintiffs asked Barrett (the Justice who hears motions from the 7th Circuit) to issue an injunction against Indiana University's policy while the plaintiffs prepare papers asking the Supreme Court to take up the case. Such motions are almost never granted, because (a) it's not clear if the Court will ever hear the case, and (b) it's likewise not clear that the plaintiffs would win even if the Court took the case.
So motions like this are very rarely granted, and the denials are usually without any explanation.
The denial of a motion like this sets no precedent; the plaintiffs can still ask the Supreme Court to take up the case. All that Barrett decided was to leave the status quo in place while the normal process goes forward.