Here is my theory..
First of all, folks who are over 55 who can be eligable to purchase this type of housing have homes of their own that they need to sell and currently have their home on the market, which most likely is not moving in some cases.
Second, folks that are over 55 do not want to be tied into a 30 year mortgage. In some cases, folks who do sell most likley are holding on there pennies and keeping it away for safe keeping.
Another reason to mention...the market is saturated with this type of housing. There is an overabundace of communites in Connecticut alone. ( I am sure you noticed)
Funny this question came up., we just did a study/discussion of this in an apprisal class I am taking. We figured there is a two parts to elderly housing. 55-70 group that are either holding on to their property, selling & saving their cash to use for a rainy day or invest in a vacation home somewhere warm. For 70+ we figured that these folks might be investing in this type of property or venturing to warmer climates where homes are cheaper (Florida)
55+ housing is a perfect fit for some and not for others. There are many great benefits of 55 + communities.
I hope this answers helps a bit.