Because they are happy all your feeders are full. Get one empty and .... 1. they will tap on your windows or peck on your head. What stories do you have to tell?
About the second month you have fed them .. they will drink out of a running hose while you are trying to do something .. or explode around a feeder in a big fight.
About this time of year .. and I wish I had pictures .. people take feeders out in the desert on flight paths and set up and give them a drink of sugar water in a place where they sorely need it .. how neat.
We use turbo natural sugar .. go back to the cheap stuff at your own risk. These little suckers play for keeps.
If you get too far from the stone age .. things go haywire.