Most people are not into the hobby enough to even think about mature media. 90% (or more) of the aquarists out there only know what the guy at the fish shop tells them. If he wants to sell them a bottle of bacteria guess what's going to happen, they are going home with a bottle of bacteria.
I am just saying why retailers don't. It can be a pain, not worth the effort, and there are more cost effective ways of helping to start a tank. I have never had a customer ask about buying mature media.
If that's what's promoted, that's what 90% (or more) of the people are going to ask for. If it isn't promoted it will rarely if ever be asked for. On this forum you have the 10% give or take that will look beyond their local shop.
No doubt their measures of starting a tank are more cost effective, from a business point of view. I have no problem with a business running as efficiently & profitable as possible, as long as the well being of animals is the first thing taken into consideration. The problem is to them fish are usually nothing more than product, the same as a bottle of any other product on their shelves. They themselves are nothing but the 90% (or more) that listen to what they are told by an individual source. So much for independent thought, continuing education, and the chance that they may come across a better way of doing things. All too many shops think like this, it’s no wonder they struggle when the economy takes a downturn.