Let’s consider the following two fairly popular segments in my area - they are the same segment but in opposite directions:

 

Even though these segments are on literally the same trail that crosses the hill, one of them can be synced as a live segment and another one can’t. Both of them contain both uphill and downhill sections, but the two ends of the trails are at slightly different elevations, so it ends up having a bit more climbing than descending in one direction than in another.

Do you think that it is arbitrary that Strava allows one of these two segments to be synced but not another? Does it even make sense to apply this limitation to running segments?

To give you another extreme example, here is what Strava considers to be a flat segment and allows it to be synced to my running watch - this literally goes over 3 mountain summits and back down. And it totally should be allowed - that what’s makes segments so great for trail running where the terrain is inevitably mixed.
 

But what is unreasonable is that this too would be arbitrary called either uphill or downhill segments depending on relative elevations of the segment start and end.