how often do you buy or sell something on craigslist and coins are involved?
1. Vending machines
2. Giving change to folks on the street
Also, plenty of people, for whatever reason, pay cash at stores; coins are needed there, of course.
And finally: for better or worse, cash is anonymous. Until a dependable replacement that is also anonymous comes along, people won't switch from cash.
cash is in general, but not coins.