A lot of it has to do with the way too many cyclists ride, and the resentment it causes. Riding on the sidewalk when there are bike lanes, blowing through stop signs and stop lights, both solo and even moreso when in riding in packs, cutting all the way across the road to turn without using any form of signaling, etc. Doesn’t excuse killing them, or hitting them, but 100% of people have suffered through that behavior, so it’s an easy case to make to a jury that the bicyclist was also at fault, regardless of the particulars of any accident. Plus, usually no video evidence to dis prove what the driver says happened.
Drivers hate pedestrians, pedestrians hate drivers, everyone hates bicyclists.