Do you hear what I hear?

The ring tone on my cell phone is just a standard cell phone ring - not one of those ones that sounds like a house phone, not some poor version of a classical song and not a downloaded ring tone. I recognize that personalizing things is great fun, but I find that people who personalize their cell phone ring tone generally seem more embarrassed than proud when it sounds off in public. You'll be riding the bus when "thunderstruck" by AC/DC blares loudly from some girl's purse; a few people turn to see whose phone is ringing, the girl's face turns red and her eyes widen in panic as she fumbles to find her phone and click the silent button. What I would like to know is, if these people are so mortified by their ring tone, why do they download it in the first place? 

The woman next to us at the baggage carousel last night had an obnoxiously loud ring tone- I don't remember which song it was, but I can still see her plunging her arm deep into her purse, awkwardly glancing side to side at the people with a shocked and embarrassed look on her face, as if to say, "oh my god I am SO SORRY....I had NO IDEA this thing was in here. And that song....my word, I certainly didn't choose that!" Clearly some stranger put their cell phone into her purse. Clearly.