If you ride 20 mph on a road with 35 mph traffic, going the opposite direction is a 55 mph closing speed. With traffic is only a 15 mph difference.

Not to mention people typically only scan for what they expect to see. My city has some bike lanes that go in both directions on one way streets. No way I use the bike lane going in the opposite direction because few people will be looking in the oncoming direction when at intersections.

Walking in the opposite direction makes sense because there is minimal difference in the closing speeds and a person can step sideways off the road to avoid danger.