It seems autism has become a sub-industry, churning state and national funds not to mention the research and grant monies involved. Since the schools are involved to a degree in referrals and special education money there has to be an element of self propagation now (and hence over diagnosis.)
Schools don't get a lot of money for autistic children, or for any disabilities for that matter. Only 40% of federally mandated special ed money is actually received by schools - the rest comes out of their general fund. Most schools see an encroachment on their general fund from special ed.