They indeed don't say "normal" but refer to them as neurotypical and the ones with adhd, autism and the likes are neurodivergent. Yeah for sure it is normal not to be interested and not finishing them and also not be able to focus but if happens A LOT of times then it is something different. A psychiatrist have said in neuroscience, there is a theory that neurodivergent people are the hunter type of people in the ancient times. The being-distracted and master-of-none is a necessary trait of hunters before so they'd be able to catch preys easier and be more vigilant for safety. Of course in this society that trait is not needed anymore so it is not the norm.
It is a bunch of shit for neurotypical of course cos they don't know how it feels like exaclty. Those things can't be controlled. Neurotypical people have it easy in this society cos the system is built for them. Who wants a person who knows 100 hobbies but leaves them even they master it in days right? No matter how successful they are with it they're just over it? Those who literally can't focus despite the silence in the environment? Those who literally have music in their heads 24/7 and some random fleeting thoughts that literally don't go away even in sleep? Try to talk to them and you'll see most of them can't even maintain eye contact for 2 seconds.
I don't know where you are from but among the people I meet in my everyday life, at least 90% of them have the same traits and they can't relate to any of those "symptoms" above. That is of course making sure other mental illnesses don't contribute to those symptoms and they were present since birth.
The research around the subject is indeed not that great yet but that’s the only explanation so far for the different traits and why these people turn out to have these regardless of how they’re being raised.
Unless you are a neuroscientist and has done years of research, saying that these are a bunch of shit just because you think they are “normal” traits without further explanation is a bit ridiculous. It’s like saying autism and tourette’s are also a bunch of shit and made up.