There is strong evidence to suggest that Bernie Sanders stayed in the 2016 race long enough to earn a buyout for his support (More importantly, the votes and donations of his supporters) . He knew the DNC had rigged the process so that Hildabeast would be the eventual nominee ...and yet..he kept campaigning until he got what he was after - the buyout - vacation home on the lake (his 3rd, BTW) and no prosecution of his wife's student aide fraud.

I believe that Biden is following the same model - he knows he is toast vs. PDJT but, being the ultimate government grifter, he's staying in the race until enough of the big money democrats pony up enough dough to make him decide to resign his office, release his delegates, and live out the rest of his life "spending quality time with his family". The longer he stays in the race and the more embarrassing he is for the democrat brand, the higher the price he's asking for is.