Well, I tell you, I also used to think that one person can keep many birds happy but I no longer believe that, either. Well, let me rephrase that, I believe that a single person can keep a lot of birds happy IF these birds are aviary species living in flock OR if there are a number of bonded pairs and just one or two single ones but, if we are talking about large species that are deeply imprinted to people and not to other birds, nobody can. Because it's not a matter of infrastructure, money, time, willingness or anything that can be acquired or worked through, it has to do with a person having only one body and not being able to split him/herself several ways. All parrots are, essentially, one-person pets so, although they will establish relationships with other birds and/or humans, they would cleave to the chosen one and would resent sharing him/her tremendously. And that's the reason why I work so hard to get my birds to mate-bond to another bird.
So when you hear about people with a large number of birds, you are talking about birds that are not really as happy as they could be. It can't be done. Not to everybirdy's satisfaction.