I assume you mean that it’s not economical to recycle them. They are large but fairly light, not enough scrap value to make transporting them to a processing facility worthwhile. Wonder if there is a business opportunity here, get the company to pay for disposal, develop a way to crush them on site, sell to scrap yard.
I guess technically you're correct. Pretty much everything is recyclable at some level, but not necessarily at the level people might think.
The issue with windmill blades is that they're largely composed of composite materials.
Thermoplastic materials can be ground down to small particles and injected into molding machines with virgin composite materials, but the end result isn't going to be exactly what the original was...it'll be a different composite formulation of necessity.
And even so, you'll still have to dispose of the next blade which "recycled" some of the original composites, and that process itself will be different as well. Because you can't necessarily infinitely recycle any given material because the recycling process itself alters the original material.
An example of different recycling characteristics would be glass and paper.
Glass can essentially be infinitely recycled. Nothing about the process of making glass is really different from one to the next recycling event.
Paper, however, cannot be infinitely recycled. Paper requires certain fiber characteristics and when you recycle paper, those fibers are changed. This is why you don't, for example, see paper products like copy paper saying "100% post consumer content". It's always a fraction of the paper content which is recycled paper, not the whole.
So yes...it's a matter of economics. And by "economics" I don't mean just "money". There's more to economics than money.
Economics is a measure of the relative worth of something based essentially on how much work is required to produce it. Time and effort, if you will. Money is just one symbolic system by which we represent the relative value of services and products.