This is a result of a SCOTUS decision. SCOTUS membership is determined by the president and control of the senate at the time of vacancies. Neither of those are influenced by gerrymandering.
At the core of it this comes down to 2016 when a larger than typical number of people on the left lied to themselves and said “eh, they’re all teh same” and tossed their vote at a third party or just didn’t vote at all. Following that, SCOTUS went from a 4-4 tie (with 1 vacancy) to 6-3 conservative advantange.
I wouldn’t blame laziness, but instead a combination of apathy and people who are more interested in ideological purity than in accepting the available-better such that they would rather complain about the unavailable-best.
RBG refusing to retire in 2012-2014 also shares blame. She could have retired then and the court would be 5-4 instead.