A whopping 76 percent of Obamacare-eligible individuals who earned between $11,770 and $17,655 annually actually signed up for a plan this year on the federally run insurance exchange HealthCare.gov, which serves 37 states, Avalere found. That income group represents the low end for qualifying for Obamacare subsidies, and as a rule those people would receive the largest amount of financial aid.  But there were steep declines in the next two income groups, even though those people receive not only help paying their monthly premiums, but as with the lower earners remain eligible for financial assistance to cover out-of-pocket medical expenses.  Just 41 percent of eligible people earning between 151 and 200 percent of the federal poverty level bought HealthCare.gov plans. And just 30 percent of eligible people in the next income group, earning up to 250 percent of the poverty level, bought such a plan.  Only 16 percent of eligible people who earned between $35,427 and $47,080—the high-end Obamacare subsidy recipients—bought a HealthCare.gov plan.  And when the subsidies weren't available, because a person earned more than $47,080, the participation was far lower.  Just 2 percent of eligible people above that income enrolled in a HealthCare.gov plan, the Avalere analysis found.  Read MoreObamacare windfall: Big drop in uncompensated care  "Virtually all of the people signing up for this are people who receive subsidies from the federal government," said Avalere Health CEO Dan Mendelson.  "A lot of the higher-income people are not participating in this," he said. "The exchanges are primarily a low-income benefit. ... The people signing up for these benefits are the ones that are heavily subsidized."  Mendelson said the findings are significant, because "it shows sort of a lukewarm embrace" of Obamacare among the people its meant to benefit.  The findings also suggest that the penalties for not having health coverage are less of an incentive for people buy Obamacare than the subsidies are.
Lower-income earners were much more likely to sign up for HealthCare.gov plans, higher earners were cooler to the Obamacare marketplace.