It's 5-4 along ideological lines, of course, and it's pure cruelty towards transgender soldiers. NY Times:

Advocates for transgender rights welcomed the court’s decision not to hear immediate appeals from trial court rulings blocking the policy.

“In declining to hear these cases, the Supreme Court saw through the administration’s contrived efforts to gin up a national crisis,” said Jennifer Levi, director of the Transgender Rights Project of GLBTQ Legal Advocates & Defenders.

“Unfortunately,” she added, “the court’s stay of the lower courts’ preliminary orders means that courageous transgender service members will face discharges while challenges to the ban go forward. The Trump administration’s cruel obsession with ridding our military of dedicated and capable service members because they happen to be transgender defies reason and cannot survive legal review.”