I wouldn't clump all of those together in the same bucket of this phenomenon. Housing and UBI are both highly political. PHP is a tech-related technical topic.
And personally I would clump the Google one as an actual "movement" that is awakening which needs critical mass to actually move forward. Not only that, but there is an element of powerlessness when it comes to such a topic and repeating things helps solidify and project the opinions to a greater audience. I.e. I feel those behaviors need to be known so I'll repeat them wherever I can.
To use another analogy: We've been doing a global search and we've found a reasonably good local-optima and now we need to explore the local search space for everything we can find on the topic. If not to find a perfect solution but at least to enumerate every single piece of info and nuance we can find.
All these subjects just repeat the same old arguments but just give a new set of people the opportunity to repeat them.
This has been how HN has always been, it's not more redditified on these subjects now than it was before.