There is an element of scale here. The individuals you are talking about have a limited impact. But the oligarchs aren't just individuals, they are billion doll

There is an element of scale here. The individuals you are talking about have a limited impact. But the oligarchs aren't just individuals, they are billion dollar institutions that are directly tied to the government in question. Or to put it another way, Osama bin Laden didn't get much due process. But that is the difference between (allegedly) committing a crime and being a threat to a government. Alleged criminals get due process, threats get "dealt with", for some given value of "dealt with". Of course then the danger is that governments will see threats that aren't really there and try to turn people into threats rather than criminals to "deal" with them. But to my mind that is an argument for better oversight of the use of the tools that governments have, rather than just removing the "threat" toolkit and leaving only the "criminal" toolkit.