I don't know for sure. Perhaps it was because the Republican Party was all tapped out, giving their support instead to their preferred "more moderate" candidates like McPherson. McClintock was outspent 5 to 1 (running against a candidate that appeared to be moderate), and came within spitting distance. McPherson was outspent only 1.6 to 1 and couldn't beat a Mexican separatist. McPherson got lots of financial support from the party leaders while McClintock got little.
Candidate Vote Pct. Spent($MM) LT GOVERNOR RACE - 2002 Cruz M. Bustamante Leftist Democrat 49.5% $4.6 Bruce Mc Pherson Moderate Republican 41.8% $2.8 CONTROLLER RACE - 2002 Steve Westly Moderate Democrat 45.4% $10.6 Tom McClintock Conservative Republican 45.1% $2.0