Or it could be because Obama is ahead of the curb in terms of the Democratic Party is concerned. Obama essentially very moderately from entitlements and puts that money into investments. Why? Because the coalition that got Obama elected consisted mainly of minorities, the millenial generation, and college educated whites (especially woman). Not surprisingly the things Obama has pushed gun control, same sex marriage, immigration, and now the budget favor the priorities of this coalition.
The fact is despite Democrats being valient defenders of entitlements 3 of 5 Seniors voted for Romney in 2012. Seniors are a big part of the GOP base which is why Ryan's plan for Medicare goes into effect 10 years down the line, why Romney ran to Obama's left attacking him for the $760 billion in Medicare savings/cuts/whatever you want to call it from Obamacare saying he would put in back into Medicare. Why? Because it would gain the approval of current Senoirs.
The fact is investmenting in infrastructure, and smart education/career training investments do a heck of a lot more in promoting upward mobility and improving the economy than retirement programs do. Look I am a supporter of Social Security, Medicare, and Medicaid but I won't freak out like some my liberal friends regarding a small adjustment in the caculation of SS if it means we get the investments we need. Especially since Obama's wants protections for the very vulnerable in his Chained CPI proposal. SS is supposed to be an anti poverty program and it has worked great at that, but it is not necessarily supposed provide a comfortable living.
Putting on my polictical strategist hat here: If I am the GOP I would make an offer to Obama. Give Obama the infrastructure and education investments he wants in enchage for entitlement reform. The kicker is no tax increases only deficit neutral tax reform. If Obama wants improve the economy he may just agree that. Again as liberal I would be supportive of moderate entitlement reform only if it came with taxes and investment. Obama though wants to look good his second term and may just take a deal without taxes to make himself look good. Not saying I agree but that is what I would do from a GOP strategist stand point.
Some articles that go more in depth on this:
A New Budget for a New Party - NationalJournal.com
Obama’s budget and the ‘coalition of the ascendant’