You need to look at the strategy LaPo employs, Nichols throws the check down because it's a given gain, the objective is to avoid the 2nd and 10 situations which often lead to two and outs, stalling drives short of Medlock's range. They can't run Harris on every down, so better to pick up 5 yds. on 1st down than taking the greater risk of throwing an incomplete pass and facing 2nd and 10 with the D anticipating the 10 yd. pass. If the primary receiver is open great, but it's not always the case.
Give credit where it's due, it may be a boring conservative strategy but it does move the ball effectively and consistently which produces a majority of wins, even if some fans don't like it. I don't think Nichols gives a rat's ass about his stats. and LaPo is not in the entertainment business, he prefers to count body blows which wear down the opponent rather than throwing hay-makers attempting to knock them out cold.