Short answer: Roth was in a hurry for Michael to fork over the $2 million, so he could then have Michael killed. That's the part of the scene where he showed his anger ("The $2 million never got to the island").
Longer answer: Roth intended to have Michael killed at Tahoe after Anthony's party because it was a perfect opportunity. When it failed, Roth went to Plan B: lure Michael to Havana (where Roth was the most powerful gringo) with the promise of turning over all his Cuban gambling interests to Michael; wheedle $2 million out of Michael as "a gift to the President" (Batista); have Michael killed by Batista's military guards; keep the $2 million or give it to Batista as a gift from Roth, not Michael. But Michael never intended giving Roth the $2 million because he knew Roth was behind the Tahoe attack, and that Roth planned to have him killed in Havana. He deliberately delayed having Fredo bring the $2 million to Havana in order to make Roth impatient and show his hand. Michael used his observations of rebel activity as a way to keep Roth waiting for the $2 million.