I think the decline of Microsoft in the mid-2000's was mainly caused by them missing the boat on the two massive shifts in computing -- from desktop software to web and mobile. Google, on the other hand, is firmly entrenched in both web and mobile. Until there is a similar shift (if there will ever be one), I don't see Google stagnating the same way that Microsoft did.

They missed that boat because of a lack of vision. They lacked viaion because of their leadership. Nadella drove through some big changes in short timespan and demonstrated a keen sense of what was important for MS. E.g. applying embrace and extend to OSS is a classic MS play that neither Ballmer nor Gates was prepared to make happen long after it was obvious it needed to be done. Enter Nadella and we now have vs code, ms github, and an actual ff-ing linux kernel that actually comes with windows 10 ready to run docker and a lot of other stuff. Also Azure is now runs mostly linux and things like sql server can run on linux. To top it off, MS is now once more exciting developers. I've not seen that level of excitement about anything they do since the mid nineties. That's leadership.

Google at the same time seems to struggle to convince developers that they need to drop their fancy languages for a bastardized and outdated thing called Dart that basically can only be explained as a ginormous not invented here syndrome combined with sunk cost fallacy. Just a minor example of things Google tries that have an obvious ticking clock in terms of them killing it in favor of something else. Also what's up with having 3 operating systems for devices and dragging out picking one out for half a decade? That's Conway's law in action right there.

Microsoft didn't miss the boat on either web or mobile, they were one of the first to both. They just fundamentally misunderstood the value proposition of each because of how successful they were with Windows on the desktop.

For the web, they thought the browser was key to the web and would be what would hold all the APIs because the browser was like the OS for the web. The most valuable thing about the web ended being the graphs and connections you can create through data rather than the browser, which is why Facebook, Google, and Amazon had the most success because of the internet.

For mobile, they released Windows Mobile in 2000 but it was just a slimmed down version of Windows on the desktop. They didn't understand that mobile required a completely new UX experience and just tried to fit what they knew (desktop UX) into mobile.

They viewed both opportunities through the lens of the desktop, which makes sense, that's what made them so successful. But because of their success, they weren't capable of looking at the opportunities with fresh eyes.

Google missed cloud computing, they are only 3rd behind Amazon and Microsoft.