5-7 years ago no one took primo? Not sure about that. I've been using it since the days of the Schering Spain Primo amps. The reason its so popular now is because it works, and its readily available without the number of counterfeits there used to be. Years ago there were no UGL's that had real primo, and that isn't the case today.
You didn't seen that people used in cycles like it is now.
Now everyone is on primo or mast. 5-7 years ago mast was believed to be only for contest prep and useless otherwise and primo it was believed that it's weak and if you don't take a lot it's not worth it.
You could get real primo years ago. Pharmacom,Balkan,Primus all got primo and it was primo not test p or nothing inside. Was other ugl but those I have in my mind that was available in 2015. Balkan was available much before that year.
The reason is popular today is because the people from youtube made it popular. Like people from youtube made popular deca only cycles, or trest or dnp.
For example even Chase "promote" mast and primo.
If he would for example took only deca you will see that people will start to take only deca again more often because now no one take only deca anymore.
Instead that I'm on 3,5 g test 1,5 g mast it would have been I'm on 5g deca and the results are great because it would have been great either way what he took the trend will start again. And from there the snow ball effects. Or instead of mast he would been using trest the trest will gain some popularity again.
At one point people took dnp often now not really and that's because not it's not working because hell yeah it's works but because the influencers don't talk about it anymore and the trend died.
Deca only cycles if you remember in 2016-2017 everyone wanted to take deca only. It was a trend nothing more same as it's now with mast and primo.
Or now it's a trend with taking besides trt to take some mast or primo. Youtube made that trend also. 10 years ago nobody took mast with their trt.
Or I can continue with sarms when they were a thing or L-carnitine...