[cyphar]

The short answer is copyright law and jurisprudence. The whole purpose of copyleft is to flip draconian copyright regimes over and make them protect users instead, so the GPL generally has the most maximalist stance allowed by copyright law. If copyright law would say that combining or extending software in a particular way is not fair use then the GPL generally would render the combination GPL.

In practice, GPLv2 would not be viral in the way you describe unless you can show that all of Android is a derived work of Linux (not true). GPLv3 would require users be avle to replace components under said license which has an impact on how such an appliance need to work (though the GPLv2 does also have somewhat related text about "the scripts which control installation") but wouldn't expand the scope of code under the license, just the terms.

[immibis]

Sadly, the layperson's and lay developer's interpretation of the GPL has been watered down over the years, and the GPL wasn't maximalist enough to begin with - see AGPL, SSPL for extensions created by people who saw new kinds of linking that didn't appear to be covered by the GPL. Of course big corporations preferably use these new kinds of linking that aren't covered, which is why new licenses are necessary.