On servers there is Linux and Windows Server, with a few minor 3rds (BSD maybe?).
On phones there are 2, 3rd place quit.
In the cloud there are 2 providers in AWS and Azure. With Google a distant 3rd.
Are you spotting a trend? Seems like each platform will support 2 to 3 players, usually with one dominant, one subordinate, and possibly one or two also-rans.
When the platform is new there's lots of variety, but as the sector matures so the 2 winners emerge.
Turns out that OSs are only as good as their developer community, and developers will support 1 or 2 platforms, not more. So 3rd place exists on scraps with few users and fewer developers.
This has nothing to do with what a generation decides - each platform has a winner and a follower, and little else.
To change the OS you have to change the platform, or invent a new one. Or maybe 2nd can overtake first (chrome over firefox/ie) but examples of that are rare.
So don't be blaming a generation, the players are just the players - the game is the game.