I don’t think this is entirely unexpected. For one thing, it doesn’t do your movement a whole lot of good if it looks weaker than 2016–which it has. This and Sanders genuinely likes Biden. Biden was one of the few, by all accounts, who treated Sanders properly before Sanders had elevated himself to the national stage. While others were dismissive, Biden was legitimately pleasant. So I think it makes it harder for Sanders on both counts. He likes Biden, and obviously would rather see him elected than Trump, and he wants his movement to excel, which it really can’t if he is losing primaries by 30+% in states he won last time.