There was nothing particularly suspicious about Maxwell's death. The music was up, the noose was tightening around him, and he was about to start eating shit for the consequences of his fraud.
The people he robbed in that fraud were regular Joes who were cheated out of their pensions, not some kind of shadow-government-global-conspiracy types who have the means to remote-program your toaster to kill you.
Him killing himself is not the most surprising way out of that situation.
It's not only that he (allegedly) killed himself. It's the manner in which it happened.
First, extremely wealthy people are by and large sociopaths. It's how they get rich. They will never view themselves as responsible or deserving or prosecution. Many are so rich they never consider getting prosecuted a realistic possibility. They will use various legal means to hide assets from being reclaimed by victims. Alan Bond, an Australian entrepreneur, also raided pension funds (which he ultimately went to jail for) but he mysteriously got divorced from his wife (who got a large property settlement) before it all went south and he stayed on good terms with her even after the divorce. Weird, huh?
Second, it's weird that nobody on his yacht noticed he was gone. For hours. That... just doesn't make sense if you know how luxury yachts work. The principal or the owner will dictate the entire schedule of the boat. If they get up at 6am, staff will get up at 5am to make sure their needs are being met. Beverages, breakfast, whatever. At all times the bridge will be manned (ie have someone on watch) who will be looking out for hazards but also at cameras on the boat. They are on alert for things like a fire breaking out or a VIP being up so they can alert other staff.
So could he have slipped through that net to throw himself overboard? Sure, it's possible. It's not icnredibly likely however. Also, is that how a rich and powerful man who was once an arms dealer commits suicide? Again, it's possible but it doesn't seem like the most likely method.
Lastly, if you're going to kill somebody but don't want it to be seen as a murder, this tops the list of how you'd do it. Why? Because, being in the water is going to wash away evidence and there are multiple ways of inducing a heart attack that are essentially undetectable (eg potassium overdose). And the delay in the body being found will likely get rid of any potential evidence there too.
The people he robbed in that fraud were regular Joes who were cheated out of their pensions, not some kind of shadow-government-global-conspiracy types who have the means to remote-program your toaster to kill you.
Him killing himself is not the most surprising way out of that situation.