The reason is that are are few ways to recycle turbine blades, and what options do exist are expensive because all of the government subsidies go to prop up companies building these essentially useless things, not toward re-purposing the junk they leave behind.
The blades are made of fiberglass and glue and have no value anywhere except for windmills - and then only as long as that one is in commission. Since they are 100 to 300 feet long, they are notoriously difficult and expensive to transport so first they have to be cut up before being hauled away using specialized equipment on emissions-belching trucks to a landfill.
Christina Stella/Harvest Public Media via NPR
When even NPR is critical of the reality of a progressive darling like wind vanes, you know it is really, really bad for the environment.