Roth-Michael meeting question

Why would Roth order the hit on Frankie when Micheal told Roth at his house he would take care of it? “I’ll visit him soon.”

Michael told Roth in his home in Miami that Pentangeli was responsible for the Tahoe shooting, and that "Frank Pentangeli is a dead man." But, instead of killing Frankie, Michael dispatched him to "settle these problems with the Rosato brothers." Roth concluded that Michael didn't suspect Frankie after all in the Tahoe shooting--meaning that Michael might suspect Roth. So, Roth ordered the Rosatos to whack Frankie at the same time he was planning to have Michael killed in Havana. That way, Roth would eliminate Frankie as caporegime of the Corleones' powerful NY empire and install the Rosatos as chiefs.