WASHINGON - The Obama administration says it's getting harder to sign up those remaining uninsured under the president's health care law.

Health and Human Services Secretary Sylvia Burwell on Tuesday gave three reasons why the 2016 sign-up season will be a bigger challenge: The most eager customers have already signed up; many of the remaining uninsured are young adults who may not see the value of coverage and those who remain are juggling tight household budgets.

Burwell says an estimated 10.5 million Americans who remain uninsured are eligible for subsidized private health insurance through HealthCare.gov and state-run insurance markets.

Open enrollment starts Nov. 1. The administration is focusing on five major metro areas: Dallas, Houston, Northern New Jersey, Chicago and Miami.

The law already has driven down the uninsured rate.