Modern societies view children as dependent and innocent, being unable to care for themselves because they are not adequately developed to do so. Elderly are viewed as having lost their independence due to old age and often take a high social status as informal teachers. There are some resources for adults, however, they are fewer and far between, due to both the cultural influences as well as financial restrictions. During the '80s to '90s, government support and welfare was cut back, and continues to be at the present time, partially due to financial restrictions (i.e. Google "neo-Liberalism" if you're very interested).

I suppose the rationale would be adults are viewed as being independent and needing, at most, temporary and mild help because they only take a small stumble, not a huge fall flat on their face. They may also be viewed as trying to skip out on working. It is unfortunate, I cannot disagree with you because the only assistance seems to be when an adult is medically diagnosed as requiring so much help they are less independent.