The main reason IE doesn't adopt webkit is that IE's current purpose is to provide stability and backwards compatibility to enterprise customers. A large portion of corporations have custom built webapps to provide basic services like HR, Payroll, etc. and they rely on IE to provide consistent behavior for these services.

Should they update their apps? Probably, but it costs money to build systems like that and most corporations don't want to drop money on something that already works perfectly fine.

Adopting webkit would completely disrupt all of these services, and Microsoft would basically destroy its customer base/relations.

Alternatively, Chrome is about pushing the boundaries of what's possible on the web. It's great for new companies, startups, and small developers, but as they move fast and implement new standards / functionality they also break stuff, and unlike Microsoft it doesn't really matter to the webkit dev team if a certain medium size corporation's old payroll app no longer works because of the latest chrome update.

Different browsers serve different purposes, and IE's is to provide stability. Hence they don't adopt webkit.

(I was an intern with IE this past summer and I asked the very same question minus the last part to my manager, and this was his response)

It was sort of mentioned. Mozilla, Opera, and Microsoft all brought up that as being something they may be "pressured into" doing.

http://lists.w3.org/Archives/Public/www-style/2012Feb/0313.h...

"Discussed problem of WebKit monopoly on mobile and the consequent pressure for other engines to implement -webkit- properties."

For IE on WP7, Microsoft originally planned to support -webkit-text-size-adjust: http://blogs.msdn.com/b/iemobile/archive/2010/05/10/javascri... , but later decided not to.