For a man for whom words are what you want them to mean and truth is whatever story the public will buy, it was the natural thing to do. Morris returns with polls showing that if it is just adultery, the public will forgive him. But if it is perjury or obstruction of justice, he's dead. So out he goes, and win he does. His polls soar.
Disaster is averted.
A former Clinton aide has expressed doubts about the Morris story. So Clinton went with the polls. It was win-win. Either he would be able to stonewall forever or, if truth was finally forced out, the more time that passed, the more opinion might change. And change it did.