I've been contacted by a source close to USC to clarify why Trojan coaches didn't speak to Isaiah Rutherford (or any other recruit) during a previous spring weekend when USC hosted so many players on campus.
According to NCAA rules, recruits cannot visit colleges unofficially while 7-on-7 tournaments are in progress, until that 7-on-7 tournament is complete. That spring weekend in question was the weekend of an Adidas tournament.
So the kids are allowed to walk onto USC's campus, walk around, watch football activities that are open to the public, etc. However, USC coaches are not allowed to interact with recruits.
Unfortunately, it doesn't seem like the recruits understand these rules. I try to interview everyone who sets foot on campus and I interviewed a bunch of top flight recruits that weekend. A lack of contact with USC during that visit was regularly brought up.
As many of us know, no good deed goes unpunished! I suggest ignoring those pesky NCAA rules in the future (joke).