Why wouldn't a coach maintain contact with a recruit right until the day he signs with any team?
With hundreds of players transferring every year, by keeping contact right to the day he signs, he may think of transferring to your school. There are tons of reasons players transfer but most of the time it's assumed it's for a nefarious reason. It could simply be things like proximity to home, a greater chance to play or change in choice of college degree.
Keeping in touch up to signing day is not some tawdry act. I'm also a USC fan, and read about 5 star recruits changing their minds post verbal commitment almost daily.