I know a RIM employee that's been walking around with a Q5 as his personal phone for months. I don't know why they dropped the 'Bold' and "Curve' branding, but it seems like a pretty decent phone.
I suspect because, 'old OS is old', and that is attached to the names of those phones. Despite that, a lot of people are still buying those phones.
-As was said, the Q5 is looming, the Z & Q 10 are out, and there are more products in the pipe. They also took the time to get the hardware right.
-Previously they had some good, secure, and well integrated software but their broader software stack was pretty shit. They 'Playbook' was a OS preview, and they took the time to get the whole software stack right before the new pones hit. No 'Storm' fiasco (minus the 'now playing' bug). Their current stack is a QNX realtime microkernel, with a POSIX compatible userland that uses Qt for the interface. That gives them a tremendous amount of Android / General Linux and BSD baked right in, preventing a lot of porting and API nightmares for developers.
-Beyond the value of their hardware and the BB10 OS there is the value of the QNX OS itself. Of the companies that RIM (now BlackBerry) bought, this was the real gem. Most of their other acquisitions were about rounding out their consumer software stack, this is and was a highly successful embedded OS. (For when it's really gotta fucking work-- like your brakes or an MRI machine.)
-There's also the potential of broadening their software to other platforms.
-While I'm no fan of patent trolls, their intellectual property, and QNX's, has real value.
-They're sitting on something like 3 Billion dollars. Money that critics said they'd have to burn through to launch their new phones / OS. They haven't.
-Their new products were generally well received, and are selling reasonably well despite not burning though that aforementioned pile of cash.
-That 'haemorrhaging install base' is actually more of a very slow trickle, and they actually have reasonable prospects of new users in the developing world, and winning some market share back in the developed world.
While I'm not predicting them to rise to Apple-like heights, they're also nowhere as near to the grave as Apple was. Oh, I don't own a BlackBerry, or directly own any of their stock.
'Internet conventional wisdom', especially when there's fanbois involved, it like trying to turn a cruise ship with an outboard motor... It takes a while, regardless of what facts are in plain sight.