Important to note that the presidency is not the only thing on the line in the dispute over late arriving mailed ballots in Pennsylvania. From the Democrats’ brief:

the ballots contain votes for state races that are not implicated in this case, as RPP’s challenge extends only to votes cast in federal races. State law requires county boards to provide unofficial returns to the Secretary by 5 p.m. on November 10 and, in certain circumstances, requires the Secretary to order a recount based on those returns by November 12. See Statewide Return and Recount Directive Procedures (Nov. 1, 2020). It is thus critical to the operation of Pennsylvania’s recount procedures with respect to state races that the Secretary have as accurate as possible a count of the ballots by next week. RPP’s requested relief would upend that statutory scheme.