The traffic is a huge inconvenience, even sometimes early morning or late night, but it just isn't a big enough inconvenience to divert to an out-of-the-way airport. If you're otherwise indifferent between LGA on the one hand and JFK or EWR on the other, I could see maybe choosing one of the others. If it's going to take you more than, say, 10 or 15 minutes out of your way, it's just silly to change because of the traffic.