It is sorta like having a sign proclaiming that you have a security system installed in your house. With so many WiFi networks available in so many places, why go after something even incrementally harder to get to because of Mac addresses, hidden SSIDs, etc.?
I don't know how many WiFI networks there really are within range of my suburban backyard, but I can see six. I don't now how many there are within range of my office, but I see 10. Some are easier to get to than others.