Because Google didn't build it themselves, the about page [1] says it was built by Fi [2].

They outsource quite a lot of work like this, a friend runs a development agency and has a number of projects on the go at the moment for Google.

[1] - http://www.messagesforjapan.com/about/

[2] - http://www.f-i.com/

You can thank Marissa Mayer for all the boring UIs Google puts out. Engineers making design decisions, you know. (I'm an engineer myself, btw.)

http://www.nytimes.com/2009/03/01/business/01marissa.html