Indications were that the Democrats had just about given up any hope of winning the 2020 Presidential election back in last December. At that point it definitely appeared that they were “throwing in the towel” when they allowed Joe Biden to take first place as their next presidential candidate. Clearly they consider Biden a "throwaway candidate" just like Walter Mondale was in 1984.
Throughout 2019, ` the Democrats appeared to have no strong candidates available to run against Trump in 2020. However, given the booming economy and Trump’s growing popularity, they didn't want to run someone to lose in 2020 that might, otherwise, be a good prospect to win in 2024. The result being that Biden would lose without question and they would concentrate on legislative and local elections.