I wonder why it is called an experiment at all. In the end this just the mods upholding the part of HN guidelines [1] that I like the most:
If they'd cover it on TV news, it's probably off-topic.
The problem with having stories and comments about mundane politics is also that they bury the technically interesting comments and they make stories on the the front page go away quicker. There are plenty of other sites where one can discuss about politics. Only on HN can one discuss, for example, with Animats (John Nagle) about the shortcomings and the history of the Nagle's algorithm [2,3] or getting lessons of public speaking from patio11 [4].Mundane politic topics interfere with HN being the exception place it is.
[1] https://news.ycombinator.com/newsguidelines.html [2] https://news.ycombinator.com/item?id=9050645 [3] https://news.ycombinator.com/item?id=10608356 [4] https://news.ycombinator.com/item?id=6199544
Edit: but it's only a change for one week!