Why is HN not as popular as it used to be?

The other day i came across this site https://hn.curiosity.ai/#/trends. I didn't manage to work out properly how to use it but i analysed a handful of everyday terms. According to the graphs the amount of traffic on hn has experienced a couple of historic declines. this suggests that hn is far less popular then it used to be. I'm a relative newcomer and i like this site so this surprised me. Why is this the case? do you feel the quality of hn has gone down in recent years?