Reposting my comment from another post about this..

Maybe it's just my distrust of the whole thing, but I wouldn't put it past them to do this just for plausible deniability, while the post office still rejects everything they can in accordance to trump's wishes.. That way people will trust mail in voting, and end up with their votes rejected anyway. They get exactly what they want while still giving some illusion of fairness.

Then, after the elections they'll just say whoops! USPS shouldn't have done that, and nothing will happen.

Edit: on another article about this..

Alito wrote in his dissent that the Postal Service “has broad authority to regulate the mail” and likely does have the power to enforce Trump’s restrictions.

So ya. It's a trap.