Most (if not all) villains in the real world are villains because they are charismatic and likeable - those that are not are no, or an extremely limited, threat.

Hitler, in and of himself, is not a threat - he would be some weird, failed, artist ranting in bars about conspiracy theories. Hitler, with his charisma, and (in his specific context) likeability, is a terrifying force.

Bin Laden similarly - on his own, a crazy man with an AK-47 in a cave. However, he has the charisma, and obvious ability to speak to and unite a wide group in order to slaughter innocents worldwide.

Every dictator, cult leader, or criminal boss in history had power and was terrifying because of their charisma, and because of their following - individually, they are nothing.

Caricaturing these people as cruel and reprehensible to those around them makes them unbelievable - why does the villain who kills and brutalises those around him arbitrarily have a following at all?

There are obvious outliers - fantasy figures and superheroes who have enough power individually to dominate or destroy in a way no 'real' figure every could - but even most of those exist in universes where there are equally powerful 'good guys' who could defeat them effortlessly if not for their minions and helpers.

You have remaining the 'real world' monsters - mass murderers and psychopaths - but even they are often reported as being incredibly charismatic, able to talk people in to going along with them, ignoring their quirks, and surprisingly all of those near them when they are finally caught.

The only villains we would have left would be school shooters, and lone bombers - those who kill innocent people and then themselves in ways that appear utterly senseless... but then what story do you tell?