As mentioned earlier in this thread ... it's about licensing. It's kind of like a "franchise" (a bit of a stretch, I know!) but hear me out!!! ....... you can't put up a pair of golden arches and open up McD's. For the fabric, etc. they have licensing arrangements with people as to how it can be used.
Eg. John Deere Fabric ... you could buy it and make things to sell. However, at the same time they have given someone the rights to use their logo for commercial goods. Thus, if you are selling things, then you are stomping on their business ..... even if it's something totally unrelated, potentially the customer might buy your Bow Tucks as a Christmas gift, instead of buying a sweatshirt.
And yes, I recognize that some of the fabrics are not famed characters/logos .... though I would think the same concept applies for the others. The designer perhaps has been commissioned to design a line for someone else ... or even further businesses of their own.
Probably fits into the same realm as all the copyright laws for not photocopying from books, or photographers photos.