1) Supply of training is probably limited.
2) Not all of these folks need training. There are a lot of people who are older, but not of retirement age yet.
3) Just because those people are trained doesn't necessarily mean that there will be jobs for them. There is a flat out lack of work out there for people - people with college educations, even.
To elaborate on that last point, lots of people (most notably Paul Krugman) contend that the recession is fundamentally caused by a lack of demand. So keeping folks on unemployment, paying rent and playing XBox instead of homeless and dumpster diving helps to prop up a segment of the economy that would otherwise have to completely drop out.
Having said that, there has to be a better way - being unemployed is miserable, even if you're receiving unemployment checks and playing XBox with your free time. It just happens that unemployment benefits are easier to defend politically than government works programs of all kinds.