Comment by Animats
This may be intentional.
Road to sidewalk is a speed transition point. The transition from street to sidewalk via a tight turn here is an effective traffic-calming component to slow down bikes from road speed to walking speed. That's done on freeway off-ramps, where there's a curved section or two of decreasing radii to force vehicle speeds down before they reach a stop sign or traffic light. Same problem.
This is the most likely reason. They should have put a sign, but the ramp looks right to me if you want them to match pedestrian speed when merging into a pedestrian space.