Fucking hell lmao.
......Obi-wan had literally gone to the planet to kill Anakin to personal kill Anakin in the first place. He wasn't defending himself. He even ignited his lightsaber first. Just because Obi-wan uses an inherently defensive and counter based fighting style doesn't mean he wasn't full on trying to kill Anakin the entire time.
1. As other people already pointed out, he was sent there by Yoda and Obi explicitly said back then that he won't be able to do it.
2. I wasn't talking about lightsaber form shit that's never relevant in the movies, I was talking about the emotional strain of fighting someone in a duel to the death versus the emotional strain of finishing off a broken husk of a man who you considered your brother literally hours earlier. It's one thing to
say you're going to kill someone, but another thing entirely to actually do it.
I'm not going to deny that the prequels are mostly badly written and there's a lot of stupid shit in them, but Obi-Wan not killing off an already dying Anakin (who, as was established and outright said just before Obi-Wan left, Kenobi loved like a brother) like you would a wounded, trapped animal is not bad writing, it's a human being acting like a human being.
During the fight, every time Obi-Wan tries to talk to Anakin it's because he doesn't want to kill him and is making sure, over and over again, that there is no other way, clinging to every last bit of hope that maybe there is a scenario in which this doesn't have to end with him killing Anakin. The meme 'high ground' line is Obi Wan's last attempt to do everything in his power to not be forced to kill Anakin.
After Anakin is disabled, Obi-Wan is visibly emotionally broken and basically crying. You don't exactly make calculated, rational decisions in such a state.