The problem there is why they have such tight bottlenecks periodically- Why not just have a traditional cellar?
Perhaps. Perhaps that was one of the use cases, but the inconsistent diameter could also be the result of them being bad at digging tunnels. Digging tunnels by hand is hard (and - dare I say - scary).
Some inconsistency from poor digging can be ignored as a minor inconvenience. It is no big deal if in one section you have to duck a little. The bottlenecks on the other hand are so small that the noticeably impede progress, and some people probably could not get through them at all.
If they are not there intentionally that would be too big of an inconsistency to ignore.