To speed up the JägerMonkey JavaScript engine.

“Bing is a new contender in the search space and while I personally think it’s making solid progress, our users are not asking for it in great numbers yet. But we reevaluate our search providers regularly and we are not precluded by any arrangements with other search providers from adding anything we believe our users want.”

Translation: we don’t want another search option because it will eat away at revenues generated from our partnership with Google.