Qt was always a bad strategy. Sure, in some aspects it was better than anything native Symbian could provide, but in general it was many years behind iOS and Android UI frameworks.
For example, one of the most frequent patterns in touchscreen UI design is an infinite list of views with dynamic data loading and filtering. A lot of use cases fit into this abstraction - social media feeds, storefronts, messaging apps, dictionaries, streaming music players, etc. Android supported this pattern in UI framework from the very beginning and continiously improved it, while Qt's answer at the time was "oh, just write it from scratch".
And the fact that Qt uses highly specific dialect of C++ doesn't really help adoption.
Are you sure you know what you're talking about? Or maybe you were using a very ancient version of Qt. Today's Qt C++ and QML are extremely capable. And I'm building one of those "long lists" (ListView) in my block editor[1] that was straightforward to implement in Qt.
In case you've missed, we're talking about an operating system whose last release was twelve years ago.
The first Qt version for Symbian was around 4.6, and IIRC QML didn't even exist then. The latest was around 4.8, and it did have QML and Qt Quick, but it was too little, too late.
For example, one of the most frequent patterns in touchscreen UI design is an infinite list of views with dynamic data loading and filtering. A lot of use cases fit into this abstraction - social media feeds, storefronts, messaging apps, dictionaries, streaming music players, etc. Android supported this pattern in UI framework from the very beginning and continiously improved it, while Qt's answer at the time was "oh, just write it from scratch".
And the fact that Qt uses highly specific dialect of C++ doesn't really help adoption.