Often the receiver going deep is not the first read and is basically a decoy to clear space underneath for the primary read. Much the way a fade is thrown almost immediately, a deep ball can be thrown high and deep if the staff has seen something in the coverage that suggests the safety is cheating up or keying elsewhere and they believe they can get over the top. It's not a high percentage pass because it really is launched to a spot and you hope the receiver doesn't get knocked off his route by tight coverage and can get to it. The reward is high of course.

Also, sometimes if the receiver is running stride for stride with the DB, the QB will throw a bit short on purpose because the receiver has an advantage of spotting the ball quicker and can adjust and essentiall box out the DB. This doesn't usually get you in the end zone, but it's a higher percentage throw.

Really tough for anyone not wearing a headset and in tune with the playbook to know what the proper progression was on any particular play. We just see the result.