They thought the iPhone was just a phone, and judged it in those terms. A massive mistake that allowed Apple to walk away with over 90% of the profits of the entire industry right under their noses. Their network effect advantages didn't help them, because they were obsolete. It's like hoping the network of stables, fields, saddle makers and horseshoe manufacturers will save the horse drawn carriage from the car. The network effects that matter to smartphones are app stores, app developers and services for apps.
The iPhone vision of a hand held computer that happened to make phone calls was way broader than I could get my head around at the time. I remember predicting that there were maybe 10 apps that would ever make money on such a device :-).
Of course my phone does much more now, calling and texting being the least of it. I wouldn't go back ( * ), but I also won't go back to the cars of the 70s. This doesn't mean I hated my dad's car.
Apple invented a new phone which is not a phone as intended before 2007 and one that people liked. That's why they got so successful.
HP and Xerox are probably still good at what they used to do (I'm happy with my ZBook and LaserJet) but they are probably not where the bulk of the market is nowadays. So they seem to be fading away.
(*) Except that phones got so light and small around 2000 that they could almost fit in a closed fist and I'm missing that.
I somehow hate smartphones nowadays because of the "more is less" dimension but the iphone was a normal thing to happen.
The opportunity came because the whole industry was moribund, they couldn't see the wood for the trees. Most of us hated our phones.