That contract isn't executed until another agency decides to use that service or product. The end-user agency benefits from a streamlined procurement process but does not receive any percentage of the contract. They are generally de-incentivized from selecting an expensive contract from the schedule, all things being equal.
Contractors influencing an unfair price is still a problem, but much less so if there are other contractors offering comparable products/services at a better rate because agencies are forced to buy the expensive option. What I haven't seen is discussion or evidence that the price inflation is systemic across a schedule that would elevate this to a full-blown scandal.
As stated in other replies, this doesn't appear to be nearly as outrageous as the article is interpreted in this discussion unless the GSA is inflating costs across the board. In the absence of that, end-using agencies can just select the cheaper option.
What was eluded to by another comment is that the more expensive contract may be selected if it's perceived to carry other social value above competitors. (e.g., "If it's coming from the prestigous McKinsey, it must be accurate")
They get to ghost write their own assignment.