I went on r/SandersforPresident and they still are donating and think that he has a chance to win. Not sure if they are in denial or just haven't been paying attention to the race.
They're just holding out hope. It's understandably difficult to admit that your candidate will lose, lord knows the Hillary supporters had a hell of a difficult time with that in 2016. Bernie's campaign isn't even pushing fundraising, he's pushing donations to charities, for the record.
Hillary lost by like 40 delegates in 2016 and won the popular vote. Sanders is on track to lose by 700 delegates and polling 30-40% behind Joe Biden.