QuickOffice was a free productivity suite for mobile devices that was compatible with the Microsoft Office file formats. It allowed users to view, create, and edit documents, presentations, and spreadsheets.
When Google acquired QuickOffice in 2012, they stated that the service had “an established track record of enabling seamless interoperability with popular file formats." At the time, Google was using Google Drive for this, and it wasn’t doing such a great job.
Google aimed to use that technology with its App suite and bring an ever more “seamless, intuitive and integrated experience” to users. And that's what they did.
Google split the Drive features into separate apps - Google Docs, Sheets, and Slides. They also introduced the option to edit Microsoft Office documents (Word, Excel, and PowerPoint) without first converting them to Google's own formats.
That’s why Google’s announcement wasn’t much of a surprise. They notified users that the QuickOffice app was being removed from Google Play and App Store, and no new features were being added from then on, but existing customers could still use it.