Earlier quoted context omitted.
But at least they run everywhere.
Where everywhere is some subset of browsers in the wild and often not that consistently anywhere. I mean the web is awesome but it’s far from perfect from a programming point of view but that of course doesn’t matter for other reasons.
Yes, but it's easier to download a version of the browser that works. The alternative is for the developer to build native apps for each OS they want to support. In my experience, it's easier to build cross-browser than it is to build cross-platform.