Impediments to wide-spread adoption of functional languages

If functional languages are so great, why does virtually no-one use them? More to the point, why have relatively new languages like PHP, Python, and Ruby prospered while functional languages have failed to make inroads in their long and glorious history? I believe the answers are largely cultural, and indeed the academic culture of functional languages is both their greatest strength and biggest barrier to adoption. I'll present a simple model of language adoption, and show specific instances where functional languages fail to support it. I'll also make concrete suggestions for how functional language communities can improve, while still retaining their distinctive strengths.