Comment by d1zzy

Quite a lot of reasons. I assume you asked that because you're thinking it's used to gather information on its users. That could be one of the many reasons. At least initially it was because Mozilla/Firefox didn't want to adopt a multi-process architecture.

In terms of strategic reasons, as a company that depends on people browsing on their websites other reasons are obvious: avoid lock in that could be pushed by third-party browser makers/competitors (say IE becomes the most popular and it implements proprietary extensions that work only on their websites[1]), ensure there exists a fast secure browser so that people can keep browsing even if everyone else stops making good browsers out there.

[1] Now before you go ahead and point out how Google proposes HTML/HTTP features that get implemented in their browsers and on the server side, all such features have public specification and source code, so anyone else could implement them too. This is very different from the IE days of yore, where MS was extending IE through ActiveX. ActiveX was developed in house and they were releasing binary plugins/SDKs to develop ActiveX plugins, effectively maintaining full control over it (one would have to develop ActiveX compatible technology from scratch if they wanted it open source, with Chrome all they have to do is fork the source code).