I've been torrenting for decades (yes, 1.2 decades is still decades) and only got my first notices in the past six months. Like 5 notices for some episodes of Silicon Valley.
Optimistically, it might be because pursuing DMCA notices aggressively probably isn't worth it for media companies. That is, they can probably hire some company to farm out sending notices, but doing much past that probably isn't worth it.
And then more realistically, I probably haven't gotten many notices because my taste in media is more old stuff. I don't frequently torrent, say, recent movie releases and popular current TV shows.