Weird ringtones

I've noticed over the past few months at least three instances of someone's phone going off and playing a really odd song, something completely unexpected. In no particular order, they are:

• ~60 year old male. He was a carpenter measuring for bookshelves, suddenly the chorus from Michael Jackson's Billie Jean starts playing.
• late 30s male, construction worker, building a house. Phone goes off with a jazz classic I've heard millions of times but can't name. Take the A train perhaps?
• mid-60s woman at a restaurant with her husband having dinner in the next booth. Silence was broken by Who Let The Dogs Out. Let me repeat that. The silence was broken in a restaurant when someone's grandmother (possibly great-grandmother) had their phone play Who Let The Dogs Out very loudly.

In every case I'm left with the obvious questions of What the hell? Why that song out of every song ever recorded? and Do people even buy ringtones anymore?