I suppose that the answer is that it's hard to copyright electronics. At a component and sub-circuit level, there is nothing in there that isn't found in other pedals and it's hard to copyright the way they work together because there are almost always other ways of achieving the same result.
The other thing that he did to protect himself was to buy out every single one of the magic diodes that he used, which means that while there are copies, they will never match the exact sound (apparently...can't verify this myself).
When I started looking at this stuff was very surprised at just how open source it actually is... how many tube screamer copies are there? How many fuzzes? It's almost like the entire industry decided not to bother.
Digital may be changing that because it's harder to reverse engineer.
The part of the story that really stands out for me is the early days when he was hand making his pedals in his kitchen and interviewing prospective clients, even really big names, before he'd agree to build them a pedal. That, coupled with the goop on the boards, is something that makes legends.
(A more cynical reply would be to say that Disney has more money to throw at copyright lawyers...)