Some speculations: one of the few places left with mostly civil discussion, no algorithms, plain text, no unnecessary user interface distractions, etc.
But why now and not a few years ago? The spike appears to have started at the beginning of this year which is most intriguing to me.
No idea. Might be due to the AI hype? Or worse: bots?
I went hunting for stats of topic trends on HN as the whole AI thing has gone bananas. Looking at the "ChatGPT" keyword chart [1] the volume is crazy and seems to line up time wise. It is a correlation but not sure if it is the right one.