Many years ago when people didn't know nearly as much as they do these days, "training" techniques were less than ideal.
In some cases it would actually kill the bird
Withholding food like this might cost the bird his life or cause irreversible and very expensive to treat liver disease.
In fact, did you know that the lifespans of birds back in the 60's and 70's was half or less than it is today?
We don't want to teach our birds to fear us or that we are cruel and make them hungry, even if it does end with our feeding them.
We want our birds to bond to us and to do things because they want to make us happy.
One bird that was in my rescue org not too long ago had gone without food for periods of time so much that he would hide food in his feathers. He'd tuck pieces of pellets, fruit, vegetables, whatever he was fed would go up under his wings and into the feathers on his back. He smelled bad all the time because the food would rot and he had infections all the time from the irritation.
This poor bird was never right again. He spent the rest of his life scared that he'd run out of food.
On the other hand, the birds that are permanent guests at the rescue are given all they want of good, healthy foods and even sips of fresh fruit juice like apple, grape and carrot. They are such happy birds that trust us so much they'll at least try to do what we want, like talk, whistle, sing, shake hands, dance, even play hide and seek.
--- Also, way back when birds first became popular we had no idea they were as intelligent as they are. It turns out that just because we don't speak the same language, we thought they were dumb animals.
I expect they thought the same thing about us.
Research has shown they are right up with monkeys, dolphins and elephants when it comes to intelligence - so they really know what's going on - all we have to do is be patient.
We have to let them learn our language, while we learn theirs. Their language is mostly in actions and body language.
I'm not kidding, if you put the guideline in place that has been outlined earlier you'll find he's going to cooperate a lot sooner than making him miserable will do.
Think about it - wouldn't you respond better to being loved than being unsure of what's coming next?