Yeah, I almost feel like Vader telling the troopers to “Stop” might help with the audience head scratching. It easier to digest Vader choosing not to pursue rather than not being able to. You could argue Vader wants him to flee with his allies in hopes of it leading to other surviving Jedi, and those that are helping them hide.
On a more personal level, maybe Vader is just a little disappointed by the encounter. I imagine Obi-Wan was not in the condition he was expecting, beating him was much easier than he thought it would be, so a part of him wants to enjoy the hunt a little more.
Yeah that’s the only thing I can think of that I can actually support. I really hate the cliche that comes up in stories all the time where the villain has been trying to kill the hero, they’re about to kill them, they were already fighting and trying to kill each other, and then the villain has the ability to kill them and they decide “no I want them to suffer” or torture them. It’s just as frustrating as heroes or antiheroes who have no problem killing bad guys deciding to not kill them, just so that they escape in a couple scenes later.
If they think they can torture them for information, or they can follow them somewhere, or they’re personally conflicted about it, or they’re trying to turn them to their cause (comes up a lot in Star Wars), or they need them alive for access to something, or any of a bunch of other reasons, then great. But just suddenly twisting from methodically trying to kill someone for revenge to some weird obsession with torture just makes them look dumb.