Indeed! Predicting the future is hard. Only Warren Buffett can financially "prove" he has any skill at it, and he doesn't personally even claim such ability (instead following a set of principles laid down by Benjamin Graham, but often ignored by academia).
PC's eventually became a commodity business anyhow, and HP wasn't cut out for commodities. Commodity businesses usually flow overseas where labor is cheaper anyhow: it's not US's bag. Microsoft made its fortune on OS's and tricking companies into entrenched software "standards", keeping it from becoming a commodity. But HP was a hardware co., not software.
HP were better off as an R&D lab and "nerd tool" maker. Stay with your strength. Warren Buffett also notices that companies that deviate from their core strength tend to suffer. Do one thing and do it well. Transitions of focus can happen successfully, but are rare. Don't bet against the patterns of history unless you want to suffer the patterns of history also. (Apple is arguably an exception, but that's another long topic.)
Which then got bought by Nokia, a Nordic bastion of...something.
A review circa 1980 of minicomputer development at DEC indicated their belief (probably shared by many in the industry) that there was not going to be room for such a diversity of architectures as there were in the minicomputer age and the 1980s would wind up like they did, dominated by a few chips like the 6502, Z80 and 8086.
As it was the 1980s were a minefield. With hindsight one could imagine that DEC could have come out with a 32-bit microVAX-based PC circa 1985. (With hindsight I don't think anybody thought that it would take another 10 years for 32-bit OS to be mainstreamed) I'm sure they thought about that, but it was certain that such a product would have taken a bit out of the existing VAX business and not certain that it would have caught on.
That doesn't excuse Carly Fiorina for the later problems at HP. Remember that Carly Fiorina was involved with fraudulent accounting at Lucent in 1999, personally I lost a few thousand bucks overnight when Lucent restated its earnings in 2000. Thanks to Carly, a proud American innovator (the former Bell Labs) got bought by a European bastion of stagnation.
If justice worked for the elite, Carly would have done time in prison and certainly wouldn't get put in charge of another company, but unfortunately there is no justice, and she got a chance to run another American innovator into the ground. At least she demonstrated how tone deaf Republicans can be by thinking her experience qualified her to run for president.