Nigel Clifford is quoted as saying there were three key areas that held Symbian back:
"Unfortunately there were three things that really held Symbian back – one, having to charge a licence fee (which we eventually solved); two, not having a unified and complete UI developed with the OS; and three, the fragmented app/ecosystem community.
We wanted to have control of these last two elements but the handset vendors guarded them jealously as they saw these as differentiators for their individual devices and companies. They therefore kept these pieces in their organisations rather than allowing us to develop them alongside the OS to create a fabulous unified user experience like you get from Apple - and so make their devices more compelling and competitive in the face of the bigger threat of Android, Apple, RIM competition."
These are areas that were well known even at the the height of Symbian's success. What was less appreciated was that competing platforms were arriving that would enable faster and cheaper device creation because they were less constrained by legacy requirements and resource restrictions (or, put another way, the nature of smartphone creation changed from under Symbian's feet as the market started to scale upwards).
The supra-app store concept, which was to be controlled by Symbian, but that never saw the light of day, also gets a mention:
"The Foundation started work on an uber-store with APIs that third-parties could use to fashion their own stores from. For example, developers with five apps could make a mini-store just containing those apps. Better yet, they could sell them through the Foundation's channel without the organisation taking a cut."
Ultimately, the project was too ambitious and, in any case, would have not arrived in time to make a difference to Symbian's fate. It suffered, like Symbian as a whole, from stakeholders who had interests that did not align with what was best for consumers using Symbian-powered devices.
As in other histories of Symbian, it's ultimately Nokia that gets the blame for Symbian's difficulties, with its dominance leading to a lack of independence for Symbian (the company and the platform). The article quotes from David Wood's paper on this issue:
"Ultimately constrained by the dual role of its largest shareholder and customer [...] We believe Symbian's eventual failure suggests key difficulties in achieving platform success in the case of divided leadership. To begin with, the existence of such divided leadership suggests a broader problem of defining and operationalising platform leadership with multiple leaders. For example, Gawer and Henderson (2007) define Microsoft and Intel as platform leaders [with Wintel]; if the Symbian platform were similarly defined, then the leaders would be Symbian and ARM but clearly platform licensees played a crucial (if not controlling) role in its evolution."
The "Nokia problem" for Symbian was a well known and long running issue and it's not unreasonable to highlight it as the ultimate cause of many of Symbian's ills. However, at the same time, it is important to acknowledge that the same Nokia was responsible for much of Symbian's success.
Jo Best's article finishes by postulating that the fall of Symbian contains lessons for Nokia's Series 40 platform, which the author sees as facing the same problems as Symbian, a technical legacy from an earlier era and a declining potential user base. Both of these are true, but it's also fair to say that Series 40 faces less technical obstacles than was the case for Symbian, and is also less subject to the conflicting set of interests amongst stakeholders that fatally undermined Symbian.
You can read the full article here on ZDNet.