I'm not aware of any research on the subject off the top of my head.  I can submit several possibilities, which are my opinions:

-With the passage of the Affordable Care Act, pregnancy was no longer treated as a pre-existing condition in 29 states, and the drop in uninsured Americans as a whole to 8.6%.
-Given that there appears to be at least a correlation between seeking an abortion and economic status, the improving economy from 2009 onward.

The larger point, though, is that the reasons why people seek abortions have little to do with whether abortion is legal and expansive or illegal and non-expansive.  The reasons still exist.