The one big piece of information Aetna hasn't shared about the shutdown of its CarePass health data platform is the very one everyone wants to know: Why? Over the last week, there's been plenty of speculation about a number of possible explanations.

Three years ago, after a similar high-profile shuttering, MobiHealthNews wrote a popular post called "10 Reasons why Google Health failed," where we rounded up some of the discussion around Google's shut down of its PHR effort. While Aetna isn't in exactly the same situation as Google was, the shutdown of CarePass has produced a similar response in the industry, as people search for answers and ask whether this will spell failure for all insurer-led consumer engagement efforts. Maybe more to the point, a number of the reasons suggested for Google Health's failures have been suggested with regards to Aetna as well: failure to integrate with the EHR, lack of patient trust, and simply being before its time.

Read on for 10 possible answers to the question of why CarePass failed, suggested by various voices in the industry in the days since the announcement. 

People just don't trust their insurance carrier with their data. A 2012 report from Peppers and Rogers Group showed that only 43 percent of patients trust their health plan, 38 percent distrust it and 19 percent are neutral. So Aetna was fighting an uphill battle by trying to get patients to aggregate all of their self-tracking data and share it with an insurance company. Patients may have feared giving Aetna too much information about their personal lives could lead to higher premiums if they failed in their workout goals.

Aetna feared competition from Apple, Google. When Aetna launched CarePass in 2012, there was no obvious leader in the field of health data aggregation. The company may have seen an opportunity to get there first and become the go-to as more and more people adopted self-tracking and found themselves in need of a portal to aggregate their data. But Apple and Google, who can build their upcoming Health and Google Fit aggregator apps into new phones and operating systems, have a big advantage in that department. Aetna may have seen the writing on the wall and decided to back out.

CarePass just failed to engage its users. At the end of the day, it seems engagement was low. CarePass partners weren't getting new users from the platform. Forrester analyst Peter Mueller told VentureBeat, "When you talk to people associated with it you hear that they couldn’t get the user numbers, so they repositioned it for employers, but that apparently didn’t work either. The market wasn’t ready for it.”

CarePass was simply not an easy-to-use app. Writing for Forbes, Neil Versel points out that CarePass's average rating on iTunes was 2 stars out of 5. Users complained of use and download problems. It's easy to forget that behind the big idea of an app, no matter how solid it might be, is the execution -- and that's no small thing.

There was too much focus on collecting and storing data, not enough on analytics. CarePass never moved past being a data aggregator, and that by itself isn't enough to engage users for very long or to make much of a change in their health. This is a thorny problem for most health app makers, and one that Apple and Google would do well to be wary of as they launch their own health tracking aggregator ventures.

It didn't integrate with the EHR. Aetna wanted improve people's health and reduce their healthcare costs, but didn't want to engage too much with the healthcare system, likely for regulatory reasons. But their hesitancy to embrace health data decreased their relevance in the eyes of many critics.

There was no ROI for Aetna. When Mark Bertolini launched CarePass, he said "This is not an Aetna propriety platform. This is for everyone. Noble cause. Why not? It’ll make our economy healthier." But noble causes, when they come in the form of free apps, are a hard concept to sustain in a for-profit business. If CarePass also failed to prove it was improving the health of Aetna members measurably, it's not surprising that the company didn't want to keep pouring money into it.

Aetna's priorities simply shifted away from CarePass. At Bertolini's February HIMSS keynote, he seemed to suggest a new focus for the company: ACOs and high-touch, mobile consumer health initiatives, like iTriage. He said the highest priority for cutting healthcare costs was the chronically ill 5 percent of the population that consumes more than 40 percent of healthcare costs -- not at all the group CarePass was targeted at.

It was a victim of internal politics at Aetna. It's been suggested that the departure of Martha Wofford was a cause, rather than an effect, of the CarePass shutdown. Certainly there has been some internal shuffling at the company in the past year, and CarePass may have been tied too much to one particular advocate or two at the company.

It was overhyped but under-promoted. Everyone within the industry knew about CarePass, in large part thanks to Bertolini taking the podium at a number of industry events. But in comments and on social media, Aetna members have confessed to never having heard about it at all. It seems the company put a lot of energy into promoting the platform within the mobile and digital health worlds, but they needed more than early adopters to make a successful platform.