The tool to make a plastic model would cost $200,000 or above, but it can produce thousands, and the mold lasts for a long time. The material cost for a kit is less than $1.00, and the production of parts are fully automated and involves no human labor, once the mold is made. Price can be low thanks to the scale of production, but the company doesn't make a model, if the sales is not expected to reach a high break even point.
The rubber mold, which is used to produce a resin kit would cost $200 or less, but it can last for only 30 copies or so, then the mold starts to degrade. Resin and metal would cost ten times more, and parts are hand cast by people in a small factory. The subject they pick only sells 300 or less, so the cost per kit is very high compared to an injection plastic model. Meanwhile, the break even point can be set low, so they can produce minor subjects.
Production of Toyota Carolla is pretty much automated, but not the same for Lamborghini.
If the subject of your interest is available in resin, you are one of those who are interested in a very minor subject just like many of us, which means that you have to put up with the situation where no kit exists at all (like 5th Gen Prelude?) or available in expensive resin kit. (300ZX Daytona Winner for example)