I think it's because when you really start to break it down it doesn't make much sense.
For starters, Itachi even said that it isn't a jutsu that can really be used in a real fight (I guess Kabuto wasn't a real fight)
But when you think about it, Izanami is a jutsu that requires you to use up your eye in order to stop another jutsu that also causes you to eventually lose your eye. So it was created to stop a move that Uchiha's couldn't spam like that anyway or else they'd go blind rather quickly. I mean even Obito could only use it for like 5-10 minutes tops before losing his eye and he had Senju dna, so imagine how fast the Uchihas Itachi was talking about ended up going blind. Furthermore, it was never explained very well as far as what would happen if you were to break out of the jutsu. It doesn't seem to stop you from using Izanagi again if you wanted to later. So basically, you waste your eye on someone who's just wasting theirs anyway.
Another thing to note, Itachi's explanation didn't say that the Uchihas were fighting one another to take each other's eyes, he said they were just arguing over which outcome to use. So they were basically bickering over which way to reach the same goal, hardly worth sacrificing your eye over, which makes them seem really stupid. I mean I'm not a big Uchiha fan anyway, but even I feel like they could've found a smarter way to deal with this issue.
I thought Kabuto was pretty lame personally so I don't consider it an "asspull" so to speak, but to me, Izanami did feel like a poorly thought out idea just thrown in to do away with Kabuto. Not poorly thought out because Kabuto got defeated by it, but because I feel like it discredited the Uchiha name a little too much when you really think about it. As far as Kabuto goes, I'm sure his fanboys would've been upset if he got beat the old fashioned way even more, so they should be happy Kishi thought of a jutsu just for him