He has the opportunity.
He feels good doing it.
And he doesn’t care. About the consequences experienced by those affected.
As long as those affected are not able to affect him back, of course!
And if you analyze the whole thing in a dispassionate manner,
this is a perfectly rational behaviour!

There is a difference. Between differences.
There is a quantitative difference and a qualitative difference.

There is a quantitative difference between moral and immoral behaviours/persons. An immoral person is someone who cannot restrain themselves in certain instances. Who knows the difference between good and bad and yet cannot resist. Cannot resist doing the bad thing.
And there is a qualitative difference between a moral/immoral person and an amoral one. The amoral one’s actions are not affected by morals. That person does anything they want to do as long as they is not affected by the consequences of their doings. Regardless of whatever consequences may have to be endured by others.

Which brings us to the difference between bad and evil. Also a qualitative one.
Which difference has nothing to do with the amount of damage caused to the bystanders. And everything to do with the attitude of the perpetrator regarding their actions!

As an aside, I have to remark that we are all ‘bad’.
In the sense that all of us commit bad things. That none of us is able to completely restrain ourselves from doing immoral things. From knowingly performing ‘bad’ things. Bad for ourselves or even bad for other people.

The difference between us, normal immoral people, and the evil amoral ones being simple.

The immoral perform things which are potentially bad. For themselves and for others.
For example we smoke. Which is bad. Both for us and for all those who breathe our smoke. But the damage isn’t obvious. We might die before developing a cancer, right?
And most of us have driven a car after having enjoyed one drink too many. With no intent to commit an accident, obviously.
Meanwhile, the amoral may commit things which will certainly cause harm to other people. Regardless of whatever rationales the perpetrators invent to justify their actions. From Ponzi schemes to terrorism.

I’ve saved the juiciest bite for the end of my post.
While immoral is necessarily bad, amoral is morally neutral. Anything in between necessarily bad and necessarily good.
For instance, using weapons of mass destruction and compulsory vaccination/quarantine are amoral. Both are used with a blatant disregard towards the feelings of all those who have to endure.
The first is ‘a certain killer’ while the latter has saved entire populations… go figure!