Not a very weird way. In a global pandemic and things are changing really really fast...days seem as months and weeks as years.
Imagine due to the pandemic the elections need to be pushed a few months? or Biden gets sick as its a very public effort running for president or the dementia stories are true or the doubt gets bigger? Keeping his delegates at this point guarantees his second in line status over a cuomo or whoever for the Democrats and does now allow them (politically) to discard the primaries ... Basically he stopped campaining and not running but keeping his score in his pocket.
What you say makes sense in theory.
However, Saunders is unelectable in the eyes of mainstream America and Democrats will do everything possible and impossible to get rid of Bernie.