I think it's more of the resources available. Scratch building isn't free even if you have the tools already. I think more and more people can refer to the internet for most of the research needs and that cuts down on the need to 'buy' the research in a magazine. There are those also with the experience of scratch building that would need to make a detailed article for the magazine.
Many many times I would prefer scratch or kitbash over buying and putting a kit straight up on the layout as when you have altered it you have given it a home. As well many times you simply can't find the building or model you need to complete your scene so a kitbash at very least or for greater accuracy the scratch build is required.
I do think it's a resource issue though. The internet has a great many resources available and this effects all forms of print media. From a scratch building standpoint alone you can get views and plot plans maps diagrams of nearly everything you would want to model.
If Evergreen was smart they would start up their own magazine highlighting techniques to achieve photo real results using their products. There are a great many scratch building suppliers out there as well as tool makers that could really do a great job if they were brought on board. Scratch building goes beyond that of just Model Railroading but that would be the largest component perhaps. You could include paper in that group as well although if paper were shown to outshine styrene and I think in many cases it does that could be a problem.
I certainly think there is enough material that a magazine could be created to fill that space. 'Scratchen and Bashen" perhaps. Enough advertisers? Well you could get tools and supplies easily enough. You could even get kit manufactures as they would be able to offer those up for kitbashing purposes. All the paint and decal (if that doesn't fit supply).
I too real a the high price of kits these days. Scratch building is not only a way to cut that down but you also have the satisfaction from building a model from the ground up.. Scratch building dead pish posh.. I think there are people with more money then time and the need to have something right now settling for what they can get. Conversely there are those with little time to write articles describing their scratch build because they are busy on their next build..
Drive through modeling.. LOL
If there was a magazine devoted to it.. A bare bones no layout approach to scratch building I would buy that. As I'm just as interested in how to do something as I am great photos of what you can do with the model you have built.
Bring me a kit and I model for a day. Teach me to scratch build and I model for a lifetime..