It has been so easy to just spread fertilizer...

 How do cover crops reduce fertilizer needs.  Yes, they sequester nutrients and provide and help build humus in the soil, but you still got to fertilize for removal if you don't want to mine your soils.  I agree, they are worth every penny, but don't agree on the need for reducing fertilizer.  Nitrogen would be the exception, but even at today's prices, it is still questionable if a nitrogen producing cover crop is cost effective, and most likely will need supplemental nitrogen fertilizer to attain good yields.