Even Apple had quite a portion of luck, getting the right decisions with NeXT acquisition, with the remaining money they had left.
There is a very long road to Google losing dominance. It will happen because everything dies but I would bet that's a long way away.
Most companies reach a size and tenure where they are still trying to grow by a certain percentage every year. They had grown year after year, but as they saturate the market or the market starts to shift they can't grow at the same rate they once did. As they turn into a stable dividend type company ideally growth should more match general market growth, but still growing.
Google makes a lot of its money from showing ads to those using search. They are facing your classic innovator's dilemma. The upstart that can't do 1/100th of what you can, but that one thing it can do it does so much better and they start taking customers and they start climbing that classic S curve of growth. Many of these companies built themselves internally for growth, not for sustainability. Internal incentives cause them to bleed the smartest and brightest & outsource whole departments rather than simplifying. Layers of bureaucracy slow down everything further letting those scrappy startups go after opportunities that the old guard couldn't.
No one thinks Google will go from 23B to 0 by next quarter, no the thing they are talking about is when companies like this don't go from 23B to 25B, but instead to 22.9B.
Y Combinator teaches startups all about the beginning of the diffusion of innovation because that is what is most important. I could probably give a little class on the other side of it, call it the missing lesson or something fun. The value isn't in learning how to not get into the same trap, but to understand your competition better and how to learn what is most likely going on internally and how to exploit it.
Yeah, this is why things get shitty.