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.
However, not all of our downstreams could, however. So it's also a practical consideration.
Also, some left over anger from the early days when BSD software would sometimes have the copyrights removed and be GPL'd. Thankfully, all the old cases of that were resolved years ago.
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.
Except it's easier to just use software where there's not a compliance issue. Regardless of the altruism of the GPL licensors, easier is a competitive advantage. It's taken about 15 years from the initial busy-box suits for supply chains to catch up with the proper provenance so that downstreams know they are getting the proper sources.
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.
Having been on the other side of this (a GPL shakedown that was improper), I'd say it's more than just FUD.
The GPL is cool and all, but it isn't all roses and sunshine.
Warner