I can’t understand what possible reason there could be for the SC to not take this up immediately. Virtually everyone agrees that they will have to take it up eventually. And it’s not like there’s a lot of new legal ground being broken in arguments in the intermediate steps. ISTM that the arguments for and against are already out there. Meanwhile there’s an uncertainty that only the SC can settle.
There may be a lot of debate and political rhetoric, but there is not a lot of legal scholarship covering both sides of the issue. Plus, this is not an issue that has bubbling away in the lower or state courts for years.
Essentially, SCOTUS wants the appeals to happen so that it can see more material written on the issue.