The primary anti scalping mechanisim Valve employes is randomizing delivery order. Being in line first because you have the fastest bot does not guarantee getting the goods first.
The original commentator is complaining they can't join the waiting list multiple times for the express purpose of "increase your chances of getting one in the first batch". That would give scalpers a potential way to get more of an advantage. And runs directly counter to anti scalping.
You are complaining you can't decide what you want once you get through which is a different issue. Though allowing that would likely make waitlists much more complex