There are lots of decent signals out there if someone did want to track it: standard site/search term tracking, the number of leechers of torrents, activity in pirate subreddits/discords, installs of Jellyfin/Plex servers etc.
FWIW I can't say I have noticed any radical increase in popularity. The number of Leechers on the most popular piratebay torrents are only in the 100s so I assume it's very niche. I suspect that "playing an .mkv file" is already too technical/clunky for much of the public compared to using streaming app. Let alone setting up a seedbox and media server behind a VPN or whatever for the best experience.
I think (from my and my friend's behavior), that a lot of movie streaming has moved away from torrents and onto free streaming sites. There's no longer any reason to download a movie you're going to watch once, and it's harder for ISPs to track you down.
Anecdotally, I've found myself doing it again. I used to when I was young, but totally stopped up until about a year ago. Illegal streaming sites have become impressively good. Better UX than Netflix.
FWIW I can't say I have noticed any radical increase in popularity. The number of Leechers on the most popular piratebay torrents are only in the 100s so I assume it's very niche. I suspect that "playing an .mkv file" is already too technical/clunky for much of the public compared to using streaming app. Let alone setting up a seedbox and media server behind a VPN or whatever for the best experience.