I’d say creating a new mobile device is more easily possible today than at any time in the past, and in fact can be done on a relatively modest budget. [1]
Take for example Purism, maker of the line of Librem devices, which has raised a few million dollars over the years and has about $1 million in revenue.
[1] - https://medium.com/os-alternative/2020-will-be-the-year-of-a...
It’s not because they dominated Windows. They owned Windows, they could do what they wanted on Windows, but for something very specific. In fact, it was a key element of the case that the government had to prove before they could proceed with proposing a remedy.
>Judge Thomas Penfield Jackson issued his findings of fact on November 5, 1999, which stated that Microsoft's dominance of the x86-based personal computer operating systems market constituted a monopoly, and that Microsoft had taken actions to crush threats to that monopoly, including Apple, Java, Netscape, Lotus Software, RealNetworks, Linux, and others.
https://en.wikipedia.org/wiki/United_States_v._Microsoft_Cor....
It's the taking actions to crush threats to that monopoly part of the equation that got Microsoft into trouble.
With Robux you can buy 100 Robux for real money and then spend 20 Robux in one game, 15 in another, 40 for a skin you can use in all games and save the rest for use in some future game that you haven't discovered yet. This flexibility makes Robux much more 'desirable' than any single in game currency.