Also, because the status quo benefitted American interests, although the crackdown is still ongoing!

"Yemen—President Ali Abdullah Saleh returned Friday to the Yemeni capital after more than three months of medical treatment in Saudi Arabia in a surprise move that could further enflame violence between forces loyal to him and his opponents. Saleh left Yemen for Saudi Arabia in June after he was seriously injured in an attack on his presidential compound in the capital Sanaa...

But the violence took a serious turn this week after a regionally-sponsored, U.S.-backed deal to transfer power hit a new snag. Saleh had repeatedly refused to sign the deal, and has recently delegated his deputy to restart negotiations with opponents on the deal. It was considered another stalling tactic by Saleh that was followed by a violent crackdown on protesters and the most violent bout of fighting between Saleh loyalists and his armed opponents...
Nearly 100 people have been killed in Sanaa and elsewhere in Yemen since Sunday...."