You're conflating inmate population with convictions, the latter being more salient in a discussion of plea deals. As another poster mentioned, these statistics are methodologically biased towards more serious crimes with longer sentences. That is, a convicted murderer or rapist goes through the trial process once (barring appeals) for a "spot" in prison that lasts 10-20 or more years. Multiple convicted robbers with short sentences would take an equivalent "spot" during the same time. They would account for a larger percentage of pleas/plea deals over time than a snapshot of carceral representation would suggest. That the figures are within a few thousand of each other, category-by-category, probably means that there are way more robbers and assaulters passing through prison than rapists and murderers. Which makes sense, if you put any stake in FBI arrest statistics.
>The 737 Max has caused a total of 346 fatalities in two crashes taking place in 2018 and 2019 [...]
I suppose that's one way of looking at it. Another is that a few hundred people committed murder in Chicago, usually with single-digit victims, and a good many of them are seeing prison time for their heinous actions. Meanwhile, a handful of high-powered executives and managers signed off on a small number of decisions that also lead to hundreds of death, along with multiple accidents that could have resulted in even more. Per alleged offender, these people have done far worse; dozens or hundreds dead each, depending on how you measure culpability. None of these people are so much as seeing the inside of a court room, let alone convictions or prison time. Boeing is not alone; officials from companies that have participated in much more destructive and heinous behavior stand with them in getting off scot-free.
It's a question of what we value our prison system(s) for. I would hope for efficient deterrence and rehabilitation. That is, sentences likely to dissuade people from committing crimes, and best efforts to prevent offenders from offending again. You seem to think that the street-level homicide rate is too high, and I'd agree. I would say that, as such murders are generally crimes of passion or disordered thinking - instinct or illness (psychological, social) rather than reason - harsh punishments are not necessarily useful in deterring them.
On the other hand, the deaths that Boeing has caused happened because of a purposeful decision-making process. It was hyper-rational. The failing was corruption. These types of moral (if not criminal) offenses stand to be deterred effectively with harshly punitive consequences; if the decision to put so many lives at risk is a cost-benefit analysis, simply make the costs outweigh the benefits. And, ideally, we wouldn't shield the perpetrators from indictment overseas, if the charges were similar to what we'd bring. What's happening is already a stain on our system - in fact, its lack of effectiveness calls into question its legitimacy - and you can add damage to international relations, that our carceral state is so out-of-wack and incapable of doing right by past and potential victims.