As a vendor or distributor, you would care. Anyone doing an OS or other
software distribution (think the BSDs, of course;
There is no legal reason why the BSDs can't distribute GPLed software; indeed, they did so for many years. Their objection is purely ideological.
but also think Apple or
Microsoft) needs to care.
Apple and Microsoft can buy up, outspend, out-lawyer, or just outwait anyone suing them for infringement. Their only reasons for not doing so are reputational.
Anyone selling a hardware device with embedded
software (think switches/routers; think IOT devices; think consumer
devices like DVRs; etc) needs to care.
Only if they are determined to infringe. Obeying the GPL's rules (most often for BusyBox) is straightforward, and the vast majority of infringers (per the FSF's legal team) are not aware that they have done anything wrong and are willing to comply once notified, which cures the defect (much less of a penalty than for most infringements). The ex-infringers do not seem to consider this a serious competitive disadvantage. GPL licensors are generous sharers, but you have to be willing to share yourself.
I saw this dynamic in action while working for Reuters; we were licensing our health-related news to websites, and I would occasionally google for fragments of our articles. When I found one on a site I didn't recognize, I'd pass the website to Sales, who would sweetly point out that infringement could cost them up to $15,000 per article, and for a very reasonable price.... They were happy to sign up once they were made aware that just because something is available on the Internet doesn't mean you can republish it on your site.
GPL (or similar "virally"
licensed) software carries legal implications for anyone selling or
distributing products that contain such software; and this can be a
motivation to use software with less-restrictive license terms.
Only to the victims of FUD. Reusing source code is one thing: repackaging programs is another.
I'll say no more about this here.