Usually when an interim coach is retained by an athletic department, a big reason why is continuity. They see something good going on and they want to keep the momentum going.
It looked like USC had a good thing going with Clay Helton down the stretch after Steve Sarkisian was fired during the middle of the season. That's a big reason why he was able to lose the interim tag and be hired on full-time. Even though they lost against the best three teams they faced after he took over (Notre Dame, Oregon, and Stanford), wins over Utah and UCLA helped them come back to win the Pac-12 South despite some key injuries late in the year.
Helton's mandate as the new coach definitely didn't have too much to do with continuity based on his first major action as the head guy. Earlier this week he let go four assistants, three on the defensive side of the ball, and is pretty much building up the staff from scratch. The only three he retained are wide receiver coach Tee Martin, linebacker coach Peter Sirmon, special teams coordinatorJohnny Nansen, and associate head coach for offense Marques Tuiasosopo.
In the long term, those decisions are likely what is best for the program. For now, though, those decisions are going stall USC's recruiting class for the time being. Keeping their top recruiter Martin and the recruiting coordinator Sirmon should help them maintain many of the current commits and keep some people from making any hasty decisions, but while other programs are busy visiting recruits, they are at a huge disadvantage with less people on the road and key positions on the staff to fill.
They don't have a defensive coordinator. They don't have a defensive backs coach. They don't have an offensive or a defensive line coach. They essentially can't answer any questions on what will happen with those positions in the next week.
The next week is crucial time too. There are six days until the next "dead period". From December 14th to January 13th, college coaches are not able to have any in-person contact with recruits at all. Written and electronic communications can happen during this time, but USC will essentially be bringing in new coaches that are unable to meet recruits while many are potentially making their decision. The major all-star games, where USC is typically well represented by commitments and where they always seem to snag a few new commitments, take place during that dead period.
It's not that USC won't have a shot at making up for lost time after, but they are just sort of stuck waiting at the moment while others are gaining ground. Even with 5 star defensive end Oluwole Betiku taking an official visit there this weekend, his future position coach is not going to be there to meet with him. It may not matter later on if somehow Helton was to convince Ed Orgeron to leave LSU and come back to LA to coach the defensive line, but if it's someone completely new without the recruiting chops of Orgeron, is USC going to be able to close on an edge rusher that they sorely need?
It's much less about keeping the class they currently have in place, which is currently ranked 15th in the nation. It's more a question if they will have a chance to make this class somewhere close to the one they had last year where they ended up being only behind Alabama in the rankings.
The only way to do that is to finish strong and they'll have to wait to race to the finish in January. While others have the next six days to secure more commitments and further build relationships with recruits, USC has to do what they can with a staff that is half-empty and hope there is enough talent left that they can land down the final stretch.