Because the butterflies would all but ensure his survival with a February 1968 POD. Nixon's lock on the nomination can be broken at the convention itself, with a July 1968 POD, which is not my OP. In any case, no RFK in 1968 means RFK in 1976.
Here's the electoral map, which translates into a Reagan sweep.
(R) Ronald W. Reagan/ Gerald R. Ford: 315 EV, 46.3%
(D) Hubert H. Humphrey/ J. Terry Sanford: 194 EV, 43.7%
(AIP) George C. Wallace/ Curtis E. Lemay: 29 EV, 9.1%
President-elect: Ronald Reagan (R)
(R) Ronald W. Reagan/ Gerald R. Ford: 315 EV, 46.3%
(D) Hubert H. Humphrey/ J. Terry Sanford: 194 EV, 43.7%
(AIP) George C. Wallace/ Curtis E. Lemay: 29 EV, 9.1%
President-elect: Ronald Reagan (R)