I guess it was for all the above reasons, and also Willie must have been really on guard. Maybe it took that long to get a shot at him.
Also John "forgave" Willie Boy. He told him that he was safe as long as he didn't testify and Willie bought it hook line and sinker. Willie was either very naïve or he thought his long friendship with Gotti meant he was safe. he didn't understand that gotti didn't care about anybody but himself. When Angelo was on his deathbed he refused to see him despite being like brothers.
