Bud didn't know that John would chicken out.
In fact, I knew John better than Bud did.
I imagine that what happened down there was, when Bud hooked up with John and told him there was a tracking job, John of course didn't say, "I am terrified. Get somebody else." Which would have been the truth.
Instead, he probably told Bud, "Let's go get Simon, he is just a five minute drive away, he is real good in the woods and he has that big pistol, two guns are better than one," something like that.