When and why did the smell of marijuana change?

Many years ago pot smoke was fragrant. Not quite fruity, but something like that and a little piney. In the last 15-ish years the smell has changed to a skunky one.

What happened and why?

(I smoked it a small number of times many years ago. I've smelled it many times in passing, and the smell has changed.)

(Although it's possible people were smoking it mixed with fruit or something, this doesn't explain it. It would mean every smoker I passed was using the same add-in, then every smoker stopped using it.)