It's a little of both, really. Low demand and my lack of time.
Even building 25 at a time, the price is what I'd consider out of hand. Then, it takes me over a year to sell through those 25. Higher quantity, better prices, but I have more stuff sitting on shelves, tying up funds.
Add to that, I can barely keep up with what I consider "core products", WPC and Stern. Nearly everything is OOS at the moment because I got blindsided by long lead times and an increase in demand. I have a bunch of stuff coming in, probably in the next couple of weeks, but then I'll be swamped, trying to test and package things, after long days at my real job.
For some reason, the Capcom kits generate way more than their fair share of support requests. That's time I could be using to build other kits, actually play my games, or maybe even participate in a league again.