According to the Kaiser Family Foundation's most recent estimate, as of March 31, 64% of Americans who were eligible for subsidized health plans sold in the ACA marketplace were enrolled.
One persistent barrier to getting the uninsured covered has been simple ignorance of what's available (though a too-large percentage of the uninsured who do check out their options find marketplace coverage unaffordable). While the numbers have improved year by year, in the Commonwealth Fund's 2016 tracking survey, 43% of the uninsured with incomes under 250% of the Federal Poverty Level were unaware of the existence of the ACA marketplace. Of the uninsured who were aware of the marketplace, 64% said they did not visit it because they did not think they could get affordable coverage there. While that was probably true for a significant number (e.g., the undocumented, those with an employer's offer of insurance, and those who did not qualify for subsidies), , a substantial portion doubtless remain unaware that subsidies are available.
While the persistent if shrinking ignorance is frustrating, it's not particularly surprising. The Congressional Budget Office always forecast a 4-5 year path to full capacity for the ACA marketplace. Enrollment is below forecast in part because CBO overestimated how many would be subsidy-eligible (Kaiser's current estimate is 14.8 million, versus a 2010 CBO estimate of 17 million for this year), partly because many who check out their options really do find the subsidies too skimpy (particularly those who earn too much to qualify for strong Cost Sharing Reduction subsidies), and partly, I would guess, because information is penetrating somewhat more slowly than might be been hoped, Right-wing hostility and disinformation, impediments to navigator enlistment thrown up by some red state governments, underfunding of outreach, and insurers' cutting of broker commissions for marketplace plans may all be factors.
Still, communicating about available benefits has always been hard. This week I was brought up short, while reading Jonathan Oberlander's The Political Life of Medicare (2003), by its account of the depth of public ignorance of the benefits provided by Medicare:
Quite simply, many of the elderly do not understand the limitations of Medicare coverage, especially with regard to long-term care. A 1984 study found that less than 40% of seniors understood Medicare's limited benefits for nursing home care, and only 13% and 225, respectively, gave correct answers about Medicare coverage for prescription drugs and mental health services....Oberlander maintains that Medicare benefits remained essentially static from enactment in 1965 to the time of his writing because the public did not understand how far coverage was from comprehensive.
A 1995 poll, taken in the midst of a Medicare reform debate that should have raised public awareness about the program, fond that fewer than half of all Americans knew that Medicare did not cover long-term care in nursing homes and only 41% knew Medicare did not cover outpatient prescription drugs (p. 52).
Like all major new benefit programs, the ACA requires patience, persistence and constant adjustment. Alas, it's not going to get them.