It's all part of a vast right wing conspiracy, using a complex network of look-a-likes, CGI footage, and (in some cases) animatronics, to dupe the masses into believing that the man's still with us, because before his death, Coulier was pulling in hundreds of dollars a year, and the heirs to his estate just aren't ready to give that up yet.
But one day, it'll all come out, and you all can join the ranks of the enlightened, like me.
The truth is out there.
RIP, DC '59-03