Who knows. Here's what it said:

Here's a response from a couple days ago on /r/buildapcsales

"Perhaps one day. But think about it this way: Us launching an app means we now have to maintain two different codebases every time we want to add a feature, redo a UI layout, etc. And with the website, if we want to change it we just do it and everyone gets the latest on the next page load. But with an app, now we have to maintain backwards API compatibility for any apps that people have on their phones but haven't updated. Also, when there's a bug in the site UI, I fix it and push it live sometimes in minutes. For apps it can take weeks for fixes to go through the app store approval process. In a nutshell, an app needs to have a very compelling use case that the site doesn't solve in order to justify its considerable extra development cost.

EDIT: We are releasing a responsive layout on PCPartPicker in the next few weeks. We’ve been working on it for over a year. It is bringing feature parity with desktop to mobile users. We chose this over an app a while back because it let us develop once for all platforms."