Because he was appointed by Trump who wanted to kill quite a few federal agencies and their cognates. Louis DeJoy is a big investor in some of the other parcel delivery companies in competition with the USPS (he's big with United Parcel Service, I think.) He's the one who trashed and discarded the parcel sorting machines in 2021, totally messing up the parcel delivery process. Lots of perishable stuff was destroyed, etc. And still they can't get rid of him, it seems.