It was more of a mindset of riders that they needed way over engineered bikes for the terrain. When lift served terrain was getting popular - everyone wanted more travel etc.
I shouldn’t complain- I got my bike 50% off when yeti discontinued the model. I think it’s swinging back a bit finally- but a lot of companies met that user demand switch and discontinued the lightweight full suspension part of their line up. As a small female who rides cross country- that was my sweet spot.
I still see that mindset, and (IMO) e-bikes have contributed to it. As with everything, people generally tend towards things that make hard stuff easier. In the dirt, that's going up hills and handling rough terrain. Why bother with fitness and skills when your bike can make those things less of a hassle? I will admit that I have a grumpy old man attitude regarding e-bikes.
One of the things that has attracted me to riding a gravel bike is that there are lots of times where you're "under-biked" for the terrain, and I love that challenge. Skills and fitness matter. I ride my gravel bike on a lot of the same roads and singletrack that I have ridden my MTBs for years. As someone who is equally a roadie and a MTB'er (I've raced road, XC, and CX), gravel is a sweet spot, combining elements of everything cycling is for me.