May 27, 2002 - World Cup Preview (Clint Mathis)
June 24, 2002 - Landon Donovan (vs Mexico in WC)
June 5, 2006 - World Cup Preview (DaMarcus Beasley, Landon Donovan, Oguchi Onyewu, Bobby Convey)
June 7, 2010 - World Cup Preview (Clint Dempsey, Landon Donovan, Tim Howard)
June 9, 2014 - World Cup Preview (Clint Dempsey)
SI has put out a World Cup US preview cover every 4 years starting in 2002, but not in '90, '94 and '98. Certainly, the US finally qualifying for a WC for the first time since 1950 did not have quite the same cultural impact back in 1990. In '94, though the bigger story was that the US was hosting the WC for the first time, SI did not have a preview cover either for the tournament or for the US team. In '98, it seems that nobody cared before, during or after, given the US' dismal performance.
It is notable that there were 2 non-WC preview covers. This means that the sporting result was remarkable enough and had a big enough cultural impact to merit its own cover. 1994's upset over Colombia and subsequent advancement out of the group stage was a massive moment for the US. 2002's run to the quarterfinals was that 2nd moment. I'd argue that Landon's 2010 extra-time goal vs Algeria was just as impactful, but perhaps their immediate loss to Ghana in the round of 16 ended their cover-chances.