Alt+Tab lets you switch to a previous window instantly. MacOS’s UI sluggishness is jarring when you’re a power user from another platform.
I think people just like what they're used to, ultimately.
Other desktop environments put the window switcher in the center of the screen (so your eyes can unthinkingly jump straight to it), you can quickly tell "hit <tab> four times to get the window I want", and your workspace wasn't disturbed with other windows you aren't interested in.
It switches between all windows within one stage