These deals (Kosovo-Serbia, UAE-Israel) were successfully negotiated because they involved a small number of parties with the United States acting only as an honest broker, not a paymaster, sort of like the way we used to do things before the "professional diplomats" took charge.
Theodore Roosevelt successfully brokered a peace to end the Russo-Japanese War. Before that, Rutherford B. Hayes successfully brokered a peace to end the Paraguayan War.