I mistyped, I meant Approach of the Second Sun. It keeps track of how often something has been cast this game
The reason it matters is that the library is a hidden zone to both players. Normally you'd know if you had the card in your deck or not, but what if an opponent exiles some of your cards face down, and one turns out to be your companion? Then you declare you're casting it, but you can't because it's not there. And maybe you scryed some cards to the bottom, so the order isn't fully randomized. Or what if you declare you're casting it, but then decide to fail to find? Your opponent isn't allowed to just go digging through your library to see if you're lying. It's just a nightmare.
With wurm, you're looking through your library already so you can verify that it's there as you cast it, and randomization doesn't matter since you're shuffling it anyway.
Those are fair points. There are rules for how to rewind something that was cast illegally, and it could handle those. I agree it likely would not be worth it.
Honestly the comp rules should just have it start in the command zone. It couldn't return anyway, its not a Commander.