It's their job to deny that the economy has improved under the Democrats; their obvious motive has to be to make Democrats look bad.
Secondly, though, the Conservatives have some truth on their side in noting that the economic recovery isn't as great as Obama and the Democrats want to claim it is. For instance -- unemployment rates are artificially low, since 1 million Americans have dropped out of the work force. Also -- economic inequality in the US continues to widen, Also -- US wages continue to be low, although the bankers are doing well, corporate profit rates are up. Also -- millions of Americans do, in fact, continue to depend not on "food stamps," but on whatever replacement for food stamps is called, under welfare "reforms" that Bill Clinton and the Republicans passed in the late 1990s.
The real truth is that western Capitalism is facing slow growth or no growth -- not just in the US, but also in Japan and the Eurozone -- that is, in almost all of the richest, longest-established capitalist nations in the world.
Capitalism "Asian Style" is doing much better in India, China, and many of the other "tiger" economies of East Asia. But even in China, the government rescued the economy by means of a big stimulus program in 2009 that has resulted in capitalist-style overinvestment and "overcapacity" -- in glutted markets -- in such key industries as steel and real estate development.
Meanwhile, many of the other Asian "tiger" economies are heavy exporters of manufactured goods to -- well, Euro and American markets. Result: the Eurozone's risk of falling back into recession is threatening the export markets of many of these recently emerging capitalist economies.
Martin Wolf, a pro-market, pro-globalization, anti-socialist columnist for the Financial Times of London, a major business publication, concludes for these and other reasons that the world financial / banking system is still at risk of another 2008-style crisis. To head off the crisis, Wolf argues, the nations of the world need to radically reform the entire global financial system; also, Eurozone governments need to stimulate their economies through more "stimulus" spending on government social programs. Also, there somehow needs to be a "rebalancing" of the world economy so that China's growth doesn't depend on selling Americans things we really don't need to buy, and on lending money to us in the form of purchases of US savings bonds, so that we'll have the money to pay for that stuff.
In other words, Conservatives are CORRECT to say the economy under Obama isn't really that great. But they're in denial about what's causing the sluggish economic performance they hate. Part of it is capitalism itself, which gets into terrible slumps of this sort every 50 or 60 years or so. Part of it is the way our capitalist economy works today -- with too much poverty, too much inequality, too much focus on capitalist bankers making money by suckering poor and middle class consumers into taking out debts that we mostly can't repay.
The solution to the US slump -- IF there is one, under capitalism -- will require "radical" change. And conservatives just won't admit that, or can't.
-- democratic socialist