The GOP House win % ranges for those who voted against the AHCA, were from 48.5% (TX-23) to 71.3% (KY-04). In TX-23, Willie Hurd won by a hair--the Libertarian got almost 5%, so the Democrat was almost able to win the district. Clinton won that district by over 3%. The next lowest GOP win was Coffman, CO-06, with 50.2%, who easily beat the Democrat since the Libertarian took 5%. However, Clinton & Obama won this district the last 3 elections.
On average, the House Republicans who voted against the AHCA won their district with a 59.4% margin, and Clinton's win margin was 45.4%. Nationally, Republicans who won their districts got 63.4%, and Clinton lost those districts at 38.4%. So while the GOP House members who voted against the AHCA had tighter win margins than other Republicans, it was not as close as I expected.
Another possible explanation seems to be the number of people that would lose healthcare coverage from the AHCA. The Center for American Progress crunched the CBO estimates for the original AHCA proposal (which failed), estimating how many people in each congressional district would lose coverage.
In fact, this result is the opposite of what I predicted. Of the 20 Republicans that voted against the AHCA, on average, about 49,580 citizens would lose coverage in those districts, compared to an estimated 53,413 who would lose coverage in all of the other GOP-held districts. In Democrat held districts, that number jumps to 57,317 coverage loss per district.
The CAP even breaks down those who would lose coverage by group: non-elderly (adults, children, disabled & Medicaid expansion), Medicaid-elderly, Employer-sponsored, and "Exchanges & Other Coverage." There were slightly more elderly covered under Medicaid who would lose coverage in the districts of the GOP who voted against the AHCA (1,880) versus the rest of the GOP-held districts (1,842), but this difference seems negligible. I found similar results for the "Employee-sponsored" losses (17,635 vs 16,240) and the "Exchanges & Other Coverage" losses (7,150 vs 6,044).
Either there is a problem with the data, or the Republicans in these districts had other reasons for voting against the AHCA.