The Supreme Court hears fewer cases than it used to, and justices write more separate opinions. Another change in the Court's docket has been that it's increasingly backloaded. The Court doesn't grant enough cases in the spring for the coming Fall, so the next term's cases get pushed later, contributing to the June (or even July) crunch of opinions at the end.
Kimberly Robinson of Bloomberg reports:
The justices have so far granted more than two dozen cases to be heard in their upcoming term, a handful short of the number needed to fill the court's first three argument sittings in October, November, and December. For a court that's hearing around 60 cases a term, that's a significant share of the workload pushed back.
The slow start means the justices will have to make up the deficit, creating a domino effect when hearing more cases later in the term means more opinions will stack up at the end, too. That's typically in late June, but last term slipped to early July. . . .
The court's rules contemplate approximately 115 days from when a case is granted to when it is argued—45 days for the initial brief, 30 for the response, 30 for the reply, and at least 10 days for the justices to review the briefs.
Because the court takes a summer recess from approximately July to October, that means any cases to be argued in the fall must generally be granted from mid-January to the end of the term. That's right when the court is the busiest, preparing for oral arguments and drafting opinions.