Blame FDR and the "New Deal".
Yes, the major impetus for the start of Social Security in the 1930s was the feeling among the ruling Democrats then that giving seniors a little government handout would cause the elderly to vote for them for years to come.
Democrat politicians have continued to play on this theme up until today, and Obama and Biden are still using it. (Since the 1960s, they have added Medicare to the list of government goodies for the elderly.)
But the only problem is that today's seniors aren't necessarily buying the well-worn Democrat line, as polls now show.