From an article posted yesterday

“Mastercard did not communicate with Valve directly, despite our request to do so,” Valve’s statement sent over email to Kotaku reads. “Mastercard communicated with payment processors and their acquiring banks. Payment processors communicated this with Valve, and we replied by outlining Steam’s policy since 2018 of attempting to distribute games that are legal for distribution. Payment processors rejected this, and specifically cited Mastercard’s Rule 5.12.7 and risk to the Mastercard brand.”