You can't equate match fixing with ball tempering. IMO, the former is a much more severe crime. BTW, I have always believed that Shakib was made a scapegoat. You can check my post here:
I have always regarded the Sunrisers Hyderabad and the Chennai Super Kings as franchises prone to shady deals. The CSK were suspended for 2 years, and only returned to the IPL in 2018. CSK is owned by N Srinivasan, while the SRH is owned by his close friend and politician Kalanithi Maran. My guess is that rather than Shakib, it is the CSK/SRH franchises that are behind the scourge of match fixing. I would say that Shakib was made a scapegoat, so that Srinivasan and Maran could escape.
Shakib al Hassan is not a child and he knew what he had to do in such instances. But here you are assuming that he didn't reported the matter to the ICC, because he never wanted to get involved in all these complexities. What I believe is that he refrained from reporting the matter to the ICC, because high ranking members of the SRH were involved in the match fixing mafia, and he was afraid that he will be kicked out of SRH and have his career ruined in case he comes out strongly against them.