Apple was the first modern smartphone with the iPhone and quickly got apps. That caused massive growth.
Google was right there too, also had apps on a modern platform. They saw what people wanted.
Everyone else was late to the party with their modern OSes. MS, Palm, BB.
By the time they arrived Android and iOS already had a big lead. It’s hard to get a company to develop their apps for your 3rd+ place platform with almost no market share. So you have no apps. So things get worse.
It was basically first mover advantage. Palm might have been OK but they were screwed over by Verizon. MS may have survived in 3rd but they kept rebooting their platform and breaking compatibility.
Now the duopoly is too strong for anyone to break into without pouring insane amounts of cash in that will likely never return a profit.
Until there is another big shift, I don’t see things changing. The current game is over, Google and Apple are too far ahead at it.