You’re right.
The trays had a groove for a CD. So placing it in the groove it would work because its edges would always fall into that groove correctly all the way around the tray.
This, however, wouldn’t work on a slot loaded drive since they worked by having a set of arms with rollers that grab the edge of inserted disc and another arm with a roller that pushed it the rest of the way in from the opposite edge when it’s inserted enough.
You can see how this worked here on a DVD drive that uses the same setup. https://youtu.be/qi3v7X6BpAA
So there’s only ever 3 slim points of contact which is fine as long as it’s a circle. Yet the irregular shape here would cause it to get partially in and then pushed by the arms into the edge/internals of the drive.
Marketing Consultant: No, King Condiment, you can’t put red in red on an ad. They won’t see it. They’ll wonder why you’re selling a gun to shoot at food.
The King: But it’s great advertising!
Marketing Consultant: No, that’s not a great marketing ad.
The King: But they can still use red for ketchup right?
Marketing Consultant: Of course. And your instructions can tell them which is for which.
The King: It’s so confusing!
Marketing Consultant: It is. And if you had hired us before manufacturing millions of these we could have told you about using another base color with red and yellow grips and triggers. But you didn’t and so here we are.