That tax is one of things keeping app quality high, and they have to pay people to screen your apps. They can offer an educational scholarship.
The tax ensures that any app developer has costs to recover. It thus drives them to do so in ways that reduce quality. At the same time it pushes away the hobbyists who may have decided to develop non-monetized versions of an app at higher quality.
(look at kids apps as example)
In other words, you have to think about that before you even release, and as a dev it doesn't really make sense to do a one-off and leave.
That’s a logic I never heard before.
(It’s a line item in corporate accounting. That’s it’s only justification. It can easily be abolished if there is any motivation to do so)
Price = commitment
As far as programmer hobbyists, one has to buy a computer, disk drives, pay for internet access, food, coffee, etc. Most hobbies and passions have non-trivial associated costs.