For the same reason you are perfectly fine with government surveillance and prohibition aggressively enforced by the State.

Just stop giving your kids money, or pay more attention to their spending habits. If you think attention to your kid is oppressive surveillance, then there is no hope for you. Apparently children are oppressed by their parents' attention and they are suddenly capable of looking after themselves, yet at the same time you are in favor of prohibition of in-game loot crates because children are not capable of looking after themselves, but you also can't look after them because that would be oppressive. The cognitive dissonance is real.