[MBCook]

Competitiveness forces candidates to balance playing to the base with not alienating the other side, lest they turn out against you.

In the current system the question is who can be the most conservative/liberal. There is little downside to pushing further because there are more votes there but few people you’ll drive away.

[boomboomsubban]

The check to that is more parties, where the most conservative/liberal has actual competition on being the most extreme.

Your change to gerrymandering doesn't make pushing for the extremes a worse strategy. Even in a perfectly split district, roughly 25% vote Democrat, 25% Republican, and 50% don't vote. That 50% is a better target than any voters on the fence.