I think it's because musky are so much of an apex predator that their curiosity gets the best of them sometimes. They see some gaudy, noisy thing in the water and the only way for them to determine if it's food or not is to bite it.
Being that a lot of muskie baits are hand crafted one at a time also, it's extremely time consuming to make a bait that size with lots of details, and when you do, you end up with a very expensive lure (see large bass swimbaits). Musky have a tendency to trash baits, so having them be really expensive, and detailed works of art when it's not really necessary, is just not cost effective and likely wouldn't sell many.
I've caught more muskie on bass lures than I have muskie baits, but none of them were particularly realistic baits. They've been on squarebills, T-rigged plastics, spinnerbaits, and frogs, none that looked a lot like anything real.