Many people from security, to the dispatcher and even the crew would have been aware of the smell...and should have questioned it. Be it with him directly, or via immediate management.
Let's not jump to conclusions. The airport authority performed drug and alcohol tests on the pilot after he was pulled and those tests came back
negative. They sent a second set of samples to a state lab but we won't know the results until after the weekend.
So at this point we don't know when (or even if) the pilot consumed any illegal / intoxicating substance. He could have appeared fine until just prior to the gate security checkpoint. He might not have smelled of alcohol when he passed by security.
Heck for all we know so far, he could have been having a medical issue.