“According to the complaint, the transaction would have enabled Visa to eliminate this competitive threat to its online debit business before Plaid had a chance to succeed, thereby enhancing or maintaining its monopoly.”
Visa tried to buy the startup building a way around Visa. The DOJ sued, and Visa walked. Visa took in about $23 billion in 2019, and it was willing to pay to make sure nobody cut into it. A merger that kills a rival before it ships is still a kill.