It's intentional. Wishlists on the Warmoth site are a huge problem, so we have had to limit them. This is because so many of our products are one-of-a-kind. If someone puts something on their wishlist, and another person buys it, what happens then? Answer: pandemonium.
A massive percentage of the products we sell are simple products with a quantity of 1. The Qty drops to 0 when sold, and never, ever gets "restocked". It just floats around forever in the database, like an asteroid in deep space waiting to strike a planet and end all life. It's a pickle.
For example, person #1 specs out a body and includes a Unique Choice lam top. Then person #2 comes along and buys a body they spec that includes the same UC lam top. A month later person #1 goes to their wish list and puts their body in their cart. Now the best-case scenario is Warmoth will double-sell a UC lam-top, and somebody is going to be pissed they didn't get what they wanted. What actually happens is an error on the second order prevents it from entering our production queue, so no one even knows about it until two months later when the customer calls to check up. Additionally, the order person #2 placed that was already underway also gets messed up. (Please don't ask me how I know this.)
Similar complications exist with any item from the showcase that gets put on a wish list.
Now I hear what you're saying: "If person #2 buys a showcase item that was in person #1's wish list, then it should simply be removed from their wish list. Easy-peasy. And they are right...that could be done. However, Unique Choice items aren't sold as a single product. They are sold as a line-item option within the larger product of a body or neck. Essentially a product inside a product.
On a personal note: This is one of those Dunning-Kruger-type things that never even occurs to outside web developers as they are criticizing our website. And there are about a thousand more.