In addition to what others have said. I'll add that some environments (Tablet, Phone, Watch, Set Top Box) are more restrictive than others (try porting a cpp app to Android sometime). Also, some systems might be missing some required libraries or have incompatible versions of those libraries (try porting a cpp app to Android some time).
Contrast that to just loading up a page on a browser.
Contrast that to just loading up a page on a browser.