Sitkowski was a highly rated croot either way but I'll concede. Let me explain it a little better for you.
Of course it happens, at all positions. Quality players get pushed out all the time if better guys become available.
By your logic, either the original evaluation takes precedence to the present, or teams are more concerned with players feelings than going for the top talent.
Team A has a great prospect committed. Another prospect grows 3" and outperforms the original prospect. Original prospect "flips" or re-opens recruitment. What do you think happened?