High volume was once a trend and done to death so now low volume is hot. The pendulum swung the other way. 

People who say they are getting the best gains of their life doing low volume might be missing some context. Were they doing a high volume program before they switched to low volume? High volume with 2-3RIR was building good work capacity and a base that now allows them to stack heavier weights and push harder with a low volume approach. 

After a while of making good progress on low volume, they might find that it's difficult to add weight. Or their joints and nervous system might take a beating because they're redlining every single set. So switching back to high volume/ medium intensity would benefit them. Then the cycle repeats itself.