1. HN has an influx of new users who are somewhat interested in technology and technology businesses, but do not have enough domain expertise to engage on discussion of technical subjects, or subjects related to startups, such as design, customer support, finance, laws (as in interpretation of legal code, not politics), etc. For them, it's easier to engage in political debate. [EDIT] As a secondary theory: politics is a subject which interests a greater number of people than an specific technical subject or business practice.
2. HN's format concentrates debate and attention on articles that get popular just after being submitted: because more pondered or technical articles take more time to get popular, they never reach the front page.
3. With no major shift in the industry in the past year, and with mostly the same players (all of which were implicated in the NSA leaks, for instance), legal issues sparked from executive and judiciary actions are getting more attention, because they make for fresher, more sensational news, and reveal unanswered questions.
I think that a simpler explanation is that politics is universal while technical topics will only be interesting to the subset of people that are affected by said technologies. Not everyone uses AngularJS/Python/Haskell/etc.