I think it's just because budgies are so common and easily found in pet stores, AND usually not hand-raised, which makes such a huge difference. Most people know somebody who has a budgie (probably purchased on impulse and then ignored) and it just sits there and chatters, and flies into a panic in its cage whenever anyone comes near. Poor little souls
Anybody who has actually known a well socialized budgie knows better, and knows they can be trusting and loyal, and hilarious, and can talk the pants off of many other species!
I choose not to live with one these days, because I find the chatter, even of a talking budgie, to be a bit too constant for my taste. Also, they don't seem to be aware of what comes out of their back ends, and when I compare that to my experience with pyrrhuras practically potty training themselves, the choice is clear for me.
Except that a healthy budgie poop is about as unoffensive as a poop can ever get. Except when a budgie is having a nap on the side of your face and poops in your ear.