The bug
The nether biome distribution seems largely unbalanced in recent snapshots, possibly due to some undocumented changes to world generation in the patch notes.
There nether seems to now largely consist of nether wastes biomes, rather than having an even distribution of all of the new biomes.
I should note that I wasn't sure if this was a bug, an inconsistency, or WAI, but I figured I'd make a bug report to get an official comment for it.