I believe that there are a couple of reasons for this.
Firstly, its advertising has sucked - to the point where I'd say that it may as well have taken its last couple of years advertising spend and burnt it in a field somewhere - it worked better for the KLF than the ghastly Nick Jojoba adverts have for HTC.
Secondly HTC have done a poor job of supporting its customers navigate the minefield that is OS updating. No user buying an Android HTC phone has any clue how many updates their phone will receive. Or how long they will take to arrive. Given that the current average length for a new smartphone contract is two years its a particularly dumb way of losing customers to leave them in the lurch when a new Android version arrives six months into that contract. Especially when that's followed by a mildly warmed over version of the phone they own running the very OS they've been denied as the next big thing.
Marketing 101: selling to an existing, satisfied customer is a million times easier than bringing in a new one. Apple understands this. HTC apparently doesn't.
HTC builds some amazingly good phones, it needs to start doing something around telling people about what their phones can do. Look at Apple and Samsung's recent adverts. Then look at the HTC 'You' campaign. A marketing campaign that looks like this is an imperative. An expensive one too, given the amount of goodwill HTC need to generate.
Secondly, HTC needs to restrict the number of devices it sells - a flagship phone, a mid-range device and an entry level device. Stagger their introductions by a quarter and you've got something to keep the media talking. Update each phone annually and ensure that each new phone and existing ones get Android updates for two years from the day the phone goes off your catalogue. If that means decoupling HTC's Sense Android overlay or removing parts of the interface to maintain performance: let the user make an informed choice.
The new HTC One, announced today, looks like a real winner of a device, with another great screen, a clever camera and a new Sense implementation. I wonder whether enough customers have enough respect left for the brand to even give it a chance.
Here's hoping they do, they marketplace would be much poorer without HTC in it.