Show a little insight. Trump makes deals. When he publicly remarked that Hillary should get a pass, it was his way of offering a deal. In all but so many words, the deal was: be a gracious loser and let me MAGA in peace, and I will spare both you and the country the divisiveness of sending you to prison.
Hillary was either not intelligent enough to understand the deal she was being offered, or she understood it but spat on it. She joined the Resistance. That was a very stupid move. Trump is under no obligation to honor a spurned deal. He’ll motivate Sessions to investigate Hillary, or if that doesn’t work, he’ll replace Sessions and go from there.
Hillary had her chance and blew it.
You and several others are trying waaaay to hard in your search for explanations. Most of the time, things are just what they appear to be.
My "insight" is that Trump is understandably irate that his campaign and administration is being raked over the coals daily, and Hillary and the Dims seem to be getting off with no scrutiny at all. Hillary did not create those circumstances herself, they came about due to several factors, the totally biased and dishonest media being the biggest factor.
If Trump wanted Sessions to begin investigating Hillary, he should have simply informed him privately.