You bring up a good point, distances are somewhat arbitrary. The reasoning is, if we double the distance run, then the running economy changes in such a way that different runners excel. However, a lot of the longer distances are run at similar speeds, making them somewhat redundant. The middle distances are underexplored.
This would be an interesting way to break it down, focusing on running speed:
200 meters (~10 m/s) 20.00
300 meters (~9.5 m/s) 31.58
400 meters (~9.0 m/s) 44.44
500 meters (~8.5 m/s) 58.82
700 meters (~8.0 m/s) 1:27.50
1000 meters (~7.5 m/s) 2:13.33
1600 meters (~7.0 m/s) 3:48.57
4 km (~6.5 m/s) 10:15
15 km (~6.0 m/s) 41:40
Marathon (~5.5 m/s) 2:07:51