Like, if Valve do want to keep item trading in (and potentially be used this way is an understatement, these are multi-million dollar gambling businesses), they could at least try to stop them.
Valve's enforcement was one round of C&Ds in 2016 (!), and then some technical measures [0] in 2024. For Valve to take heed the problem, they literally had to have a stage invasion at their esport event [1].