Okay, even taking all of that into account, it's still not an offensive system that supports 4 WR's in the same class.
It prominently features TE's and FB's on the regular, leaving room for 3 WR's to see regular PT, maybe 4 or 5 if there is an injury among the top 3 at some point in a season.
Combine limited reps in the first place with the fact that Crawford and McDoom are there in a class ahead of them, you suddenly have two (maybe three!) WR's in the same class all riding pine for 3 years.
If Harbaugh convinced these kids that they're gonna all get plenty of reps or that it would be worth it to wait until their JR year to get some shine, that's cool... but at the end of the day, two of those guys are going to be unhappy with how their careers at scUM shake out.