Because really that's what pocket money is about. Wants rather than needs.
No, pocket money is about whatever the family involved make it about.
There are lots of different attitudes and styles and views represented here.
Some parents give children more money and more responsibility to pay for their needs as well as their wants. that is no less valid than your view.
As for the not giving them money in order that they then moderate their spending on random stuff, it really doesn't necessarily work that way. DS1 has managed to accumulate the best part of £1k from pocket money, Christmas and birthday money and the odd tenner that his Gran gives him when we visit. He rarely spends anything, never asks for anything but on occasion has made himself large purchases (a TV and a laptop). DS2 gets pretty much the same although he is a year younger so technically has had less birthday and Christmas money to accumulate. He is lucky if he has much more than £50 at any given time as he will buy new PC games that his friends have etc (he has a lot of "stuff") However again he very rarely spends it on consumables such as snacks, magazines etc. and did save enough to buy himself a PC at one point.
Both brought up the same and with very different habits. I'd ideally like there to be a happy medium. I think it's important to learn to treat yourself from time to time - we only get one life and all that, but also you need to live within your means.
DH and I don't buy a lot of "stuff" either but don't have anything against it.
I don't think there is a right or wrong, just differences.