I think about this a lot too. There always seems to be a fitness trend involving classes like aerobics, yoga, pilates, Taibo, Zumba. But if we're talking about weight training, it is definitely having a moment now.

I wonder if all the instructional content on Youtube makes training with weights and weight machines more accessible than ever. I was intimidated by weights and figured it would be boring. A guy I knew was talking about his weight training and I asked if he plans things out with friends/workout buddies and he said he learns about it on YouTube. So when I finally pushed myself to try weights, I found a video. It was a petite woman (I'm a dude) and I thought, ok she looks better than I do and this routine is a nice start. And I went from there, in my forties.

My funniest theory is that dating has been getting more competitive and strength-training is good for confidence.