The reason is because other similar Google services have outpaced Orkut, leaving it with no option but to close he ten year old service.
Below is the press release being sent out by email to all those who have accounts with Orkut.
After ten years of sparking conversations and forging connections, we have decided that it’s time for us to start saying goodbye to Orkut. Over the past decade, YouTube, Blogger and Google+ have taken off, with communities springing up in every corner of the world. Because the growth of these communities has outpaced Orkut’s growth, we’ve decided to focus our energy and resources on making these other social platforms as amazing as possible for everyone who uses them.
We will shut down Orkut on 30 September 2014. Until then, there will be no impact on you, so you may have time to manage the transition. You can export your profile data, community posts and photos usingGoogle Takeout (available until September 2016). We are preserving an archive of all public communities, which will be available online from 30 September 2014. If you don’t want your posts or name to be included in the community archive, you can remove Orkut permanently from your Google account. Please visit ourHelp Centre for any further details.
It’s been a great 10 years, and we apologise to those of you still actively using the service. We hope that you will find other online communities to spark more conversations and build even more connections for the next decade and beyond.