The gap is narrowing, but it might have never been there in the first place -- insurance companies didn't have the detailed data they needed or the computing power to effectively analyze it in the past.

As insurance companies get more detailed data and the computing power to analyze it and regulatory & competitive pressure to act on that analysis, they refine their pricing structure. For some of the more finely divided groups there is a gap.

For example, there might (still) be a big difference for

18 year old single females on their own policy vs 18 year old single males on their own policy

but there might not be a big difference for

18 year old single females who are "occasional operators" of vehicles on their parents' policy vs 18 year old single males who are "occasional operators" of vehicles on their parents' policy