About 29 million people are still without health insurance, government estimates show — down more than a third since 2013. About half are eligible for subsidized coverage through the marketplaces or can enroll in Medicaid. Signing them up won’t be easy, Obamacare navigators and advocates say. Many don’t see the need for coverage, they believe it’s too expensive or they are unaware of financial assistance to lower the costs for insurance, surveys and interviews have found.