Actually, the reason is that old people who live in these communities don't want young families or children, and don't want to pay school taxes. In some states, retirement villages are exempted from paying local school taxes b/c there aren't any children to support.

Local governments hate retirement villages b/c they are not net contributors to local tax coffers: they use up more police, fire, and medical services, they rarely purchase goods (IOW, no sales tax), and they don't own property (b/c the units are "leased" not owned) so they don't pay property taxes. On top of all that, they usually oppose new development in the vicinity of the retirement village, which can freeze commercial development.