There’s also no way to profit from an execution so far as I can tell.

there absolutely is, with legal injections whoever sells them makes money, you save money as a prison by not having to house these people, and while you can't exploit them for labor, there is never really a guarantee that you can. It's a little more nuanced than this, for example solitary confinement generally makes it pretty hard to make money off of people. Death row is often a multi year process, taking many many thousands of dollars of human upkeep to keep it going.

technically you could go a step futher and say there's a broader economic benefit to killing them as you can use it as some sort of social driving pressure. Stalinist USSR for example.