Does it really take "courage" to speak up in cases like this? If anything, it's just as insulting to point out to an adult that playing loud audio in a crowded public place is inappropriate, as if they didn't know that!
It can create an awkward situation which a lot of people are averse to. For example, I wouldn't speak up on other forms of public transport, but in airports in particular I go on a warpath.
That person is already ignoring obvious social conventions. People don't want to know which other shitty behaviours they have in store.
Yes, it does take courage, the person doing it is likely to react poorly and it could easily escalate into a physical altercation.
for me, the worst offenders are men watching sports on public transportation or restaurants. I hate it, but I think different cultures have different norms.