I can't call my typical mix entirely inert, but most of my plants are grown in a rockwool, sponge rock, hydroton and medium charcoal based mix. Then, depending on the plant, I may or may not mix in small amounts of oyster shell, egg shell, fir bark and/or sphagnum.
With a mix like this, I no longer need to repot as often and overall it seems like my plants are doing better. They grow better, have more extensive root systems and they bloom more often. Part of that is simply the fact that as I become more experienced, I'm better at growing. And the better I am at growing, the bigger and robust the plants get.
As far as why inert potting mixes aren't more common, well probably nobody would know for sure. I can make some guesses. Part of it is probably tradition. There's a long history of bark and moss mixes, and if people have good success with it, there's no need to change. It also seems like price might be a factor. Even though you may have to repot less often when you use an inert mix, when you look at the price of a bag of bark/moss that many people can go to a local shop to buy, versus the cost of a bag of sponge rock, LECA, rockwool, etc that you have to order online or drive to special shops to get, the bark is just cheaper. Long term, that may not be true, when you consider how much more often you need to repot, but that probably isn't a consideration for many folks.
!! Jean
