Yeah, I think it's a bit unfair to reduce this to the indifference of DAs. They focus on getting plea deals and convictions because that's what their constituents focus on. No DA wants to squeeze out a plea deal if their constituents are going to be angry & disappointed with.
It may be how they view their role, and it may be how their incentives line up.
But it's not actually their job. I bet you know this, I'm just clarifying.