Well, if they file their taxes, aren't exempt, and don't have insurance, all of them?
I know that doesn't help you much. I found this article for the 2014 fine. https://www.rt.com/usa/310405-irs-pe...care-millions/
Unfortunately unless you are talking about a survey, the reasons behind why they paid the fine are quote varied. There are two groups of people in my estimation.
There are those who want insurance but "can't afford it" (for various reasons) and have to pay the fine, and there are those who don't really want it, and pay the fine. There is no way to know from most data collected how many fall into each category. if Kaiser or someone has done a survey, I would love to see it as well.
For me personally,
1. young single people making $45,000 so not subsidy eligible based on premium being less than 9.66% of income (or whatever it is now). Would rather go on vacation than pay the $2400 annually for basic coverage. Pay the fine.
2. middle class families caught in the family glitch. Family of four making $60,000. can't afford the $800 a month through hubby's work for mom and kids, can't afford the $800 a month cash price for mom and kids plus what hubby costs at work, 20% of the time depending on income kids go on SCHIP and even then they still can't afford the $400 a month for mom alone just to have a $6000 deductible. Pay the fine.
3. older married couple making $70,000 a year who can't/won't pay the $1200 a month for decent insurance and sure as heck aren't paying $800 a month for the $6000 deductible (each) plan with no network. Some of them are exempt, some aren't. They typically go with a short term/noncompliant policy if in good health and pay the fine.
4. younger married couples who make $45,000 together and just don't want to pay $400 a month for health insurance after subsidy. A lot of them are going to the healthshare ministries, some go with noncompliant plans at half the cost. They go on and pay the fine.
5. People who just hate anything to do with Obamacare and pay the fine under protest. this is a pretty small percentage in my estimation. there are tons of people at 151% of poverty who say they hate Obamacare until they find out they can get a plan with no deductible for $50 a month.