A lot of "legacy" companies had businesses that were doing very well but missed the boat one or more times as new things arrived. Microsoft is a good example. Windows and Office was absolutely, positively printing money. They whiffed on mobile so hard it was comical. Going back further in time, IBM got mauled in the PC business over time, even though mainframes and PCs were keeping the lights on for decades.

I disagree with the assertion that in 5 years these companies may be heavily disrupted but these darlings that preyed on the fact the incumbents were ossified, large and slow are now themselves ossified, large and slow. The cycle continues on.

In the particular case of Twitter they're being actively driven into the ground by a guy who seems determined to wake up each day and not go to bed until he's made some very poor decisions so who knows, maybe they will crash and burn quickly.

Google’s core businesses are doing just fine too.

Twitter has suffered financially but I’ve seen little evidence that they’ve lost substantial numbers of users — Twitter posts are still in news articles and sites like HN as if it’s still serving it’s original purpose despite the noise.

people treat facebook as if it were like their myspace, something dumb they did in their youth that's not longer relevant and is dying

reality is pretty different, fb business is doing great despite all their missteps

And so is googles, Facebook are spending more than $10B a year on VR. For context that is more than Nvidia's quite large R&D budget, which they have ramped up on consistently over years. Facebook has gone from 0 to 10B real fast.