Biden had a majority on the board.

TL;DR:: remember the fuckery Moscow Mitch pulled with SCOTUS nominees? They did the same with Postal Board of Governors.

Q: Why can’t President Biden fire the postmaster general?

A: Since many ballots are cast by mail, there is substantial concern about who is running the postal service and if they will prioritize ballots to make sure votes are received in time to be counted. Indeed, the mail service and absentee ballots have been at the center of debates related to electoral integrity and criticism of how Postmaster Louis Dejoy, appointed during Donald Trump’s term, has performed the duties of office. However, President Joe Biden does not have the power to fire DeJoy, even if he's unhappy with his performance.

The reasons lie in the governance structure set up for the U.S. Postal Service. Unlike most executive branch agencies which have a single leader appointed and removable by the President, the Postal Service is overseen by a Board of Governors. Under the Postal Reorganization Act of 1970 (39 U.S.C. §202) there are nine governors appointed by the president and confirmed by the Senate for staggered 7-year terms.

The Board also includes the postmaster general and the deputy postmaster. The postmaster is appointed or removed by the other members of the board, not the president or the Senate. Interestingly, the law requires that "not more than 5 of [the Governors] may be adherents of the same political party." Both the appointment process and this limitation were intended to insulate the Postal Service from direct political influence while still maintaining oversight from Senate-confirmed officials.

However, it is difficult to get people appointed to the postal board. Then-President Barack Obama sent seven unsuccessful nominations to the Senate. By 2018, there was no one confirmed to the Board of Governors as all the terms had expired without replacement. Without governors in place, the board cannot form a quorum (6 members) to officially conduct business which includes things like setting rates or approving the budget.

The lack of governors also meant there was no way to appoint or remove the postmaster general. However, the vacancies the Senate would not address under Obama were later filled by then-President Donald Trump. The newly appointed board then chose Louis DeJoy as postmaster.

There are a few options for President Biden if he wished to remove DeJoy. The president could under federal law fire the postal governors for cause. However, this requires some form of misconduct or malfeasance that may not be present. Alternatively, the president could argue under the precedent of Seila Law v. CFB (2020) that he has the right to fire any leader of a federal agency. That action would be a highly contested and probably end up in court.

The simplest solution would be to appoint enough governors who are interested in changing the leadership of the Postal Service. If enough nominees were confirmed, then a new Board of Governors would be formed that could potentially remove DeJoy. However, there is no guarantee that the new governors would choose to change the leadership, and even if they were so inclined, this takes time, and it might not happen before the election.