Here's my explanation:
American voters HATE sore losers. No quicker way to end a political career than to become one.
Thune knew this and took the gracious loser role knowing he could come back and fight another day.
His political base was rock-solid...he had won his previous statewide congressional races by huge margins.
Looks to me like he's turning out to have been pretty darned smart.
Isn't it ironic, that all of Dashle's dirty tricks to keep himself majority leader, may end up being the cause of his own demise by setting him up with a real opponent?
There were a number of people on FR who thought that Thune should have challenged the results. A majority realized that (a) you never win the seat back when voter fraud is challenged and (b) Thune would have a better chance against a Daschle whose liberal positions are well-known during a presidential election year.