And as for children, not that it is a complete correlation, but there is a lot more preparation for that. Girls are prepared for having children since they were playing with baby dolls as children. Worst case scenario, young mothers can often receive help from their parents or friends cause after all, most people end up having experience with children. People take children out in public, we meet friends with children, there may be siblings, lots of movies and books about the experience of working with children, and to some extent I bet some of it comes naturally. However, with parrots it is completely different. There are few resources, their merits debatable, few other people with parrots that we can meet in person. For all we know our neighbors could have them and we'd never know (far neighbors or close ones with super quiet parrots

). The fact is that parrot ownership (unlike dogs for instance) is a very private matter so there is little chance, unless you know someone with parrots personally, to get to see other people's birds. They don't appear much in books/movies and when they do, they are usually grossly misrepresented as a cheeky thing that just sits around and says all the right things at the right time.
No, I really do not see how someone can just jump into it and get a really difficult parrot to start. If someone gets a macaw and gets bitten insanely hard right away, not likely they will keep the bird or even be able to overcome it. At least if they'd get a smaller/less aggressive parrot they would at least have the potential to get over the biting, stand their ground, and eventually work it out. With the knowledge of how painfully a little parrot can bite, they would be much better equipped if they could bear a bite ten times the size. Someone who has never been bitten by a parrot, hardly qualifies as experienced to make a decision if they can handle/overcome big biting just cause they "researched it" and read it in a book or talked to people.
When I was buying my Senegal, I was asking "intelligent" questions like "how loud is it?", "is this a healthy diet?", "what is toxic to this parrot?". Now I find myself asking "how do I manage aggression?", "how to deal with hormonal/mating behavior?", "how do I motivate better flight recall?", "how do I socialize it to other people?". None of these questions came up or could have come up when I was buying the parrot because there wasn't much way of knowing these issues or the magnitude of them until dealing with them. All I can say is that I'm lucky that the parrot is small enough that the bites are tolerable and quiet enough that the noise isn't an issue. Now when I buy my next parrot, I am equipped to ask the breeder very serious long term questions rather than the short sighted questions we ask as a beginner.
For some people, the biggest issue may be biting, for others screaming, but for someone else it might be the poop or endless chewing of our stuff. New owners may not realize that the chewing issue will affect them most or the screaming. Some people don't care about the screaming but then can't handle the chewing or something else. We can't learn what peeves us about parrots until we've lived with them. So the requisite ownership helps us learn what we can't stand and prevents us from buying a bigger more extreme version of that. At least when we start out with a small parrot, the poops are small, the bites are small, the screaming is small(er), the chewing is less damaging. We can learn how to deal with these issues and then decide if we could handle them on a larger scale.