Why should anyone have to make a "mental shift"? The answer is not because UNIX is incompatible with other systems. The answer is more likely because Microsoft Windows is a proprietary commercial product; its sales and marketing staff have traditonally sought to discredit UNIX. Having followed Windows from 3.11 onwards I would argue that it is "different" and incompatible by design. The "mental shift" is intentional and strategic, but not at all necessary.
Why were there no plans to make PowerShell free and open source and publicly available initially? That's a rhetorical question of sorts.
UNIX as the OS that generally "runs the internet" has become better known and more popular in recent years as a result of several factors. That's why MS has to make the moves they're making. keywords: "has to"