There are things that are known, and some that are 'read between the lines'.
There was a lot of talk after spring about development, about how many guys on staff had been qb coaches and how much work everyone was putting in. Given all we heard publicly, it's very likely there was even more talk about how to improve and make sure that we would have a reasonable passing offense. It is after all what this staff is really all about. You're a team first type WR guy, so you buy in that the staff has this under control, and if stuff goes south others can step in.
This staff, at that point, still had really had very little exposure in working with JM. Remember they can only do that type of stuff during the actual spring practice and are not allowed to work with them outside that timeframe.
As it ends up, the staff's optimism does not pan out. They can't get JM over his challenges. The staff who assured the WRs it would be all good, can't make it right. To make matters worse, your play distribution angles much more toward zone reads because you actually can block, and you get fewer reps on pass centric plays.
Even though you call them N5-7, all these guys were in the 2 deep - we are literally losing 4 of the 6 guys in the 2 deep. Law was a starter. Prentice started as a freshman, and has made several starts over the last several years including this year. Henderson is really the only one who was possibly outside the bubble, and that's because he was an RB in HS and had to learn a lot about how to be a WR.