I don't think there's a big mystery about why Matt Gaetz escaped federal charges. The elite in this country, more often than not, do not face legal accountability for their actions. It's the background assumption for everyone in power, including Merrick Gartland. Sure, everyone likes to talk about equal justice under the law, and all our courthouses have that statue of lady justice with a blindfold as a symbol that justice is blind. But in fact that's not even close to true. You can see that everywhere.
In fact, that is the reason that Trump will be President again. It's why the Supreme Court ruled that he was broadly immune from prosecution, and that the Constitutional prohibition against anyone who took part in an insurrection against the U.S. does not exclude him from office even though that's exactly what he did. The underlying assumption is that it is unreasonable to exclude him from power, even when the language of the constitution points pretty clearly to that conclusion. The J6 rank-and-file can be prosecuted to the full extent of the law because they are regular people. The law applies to regulars, not the important ones. Just because Elon Musk violated the conflict of interest rules that all other federal contractors are subject to, doesn't mean that we can cancel contracts to the richest man in the world! He's the richest man in the world! That's all the explanation we need, or at least all the one we will get.
Maybe it has always been this way, I just bought into the justice is blind myth more before. Maybe this isn't so much of an age of impunity than impunity for elites is a constant in human society. That still doesn't make it right.