Robin Williams famously said 'Cocaine is God's way of telling you that you have too much money.'
and there is a lot of truth in that.
Rich and famous celebs are surrounded by people who never ever say no to them, and they live in a rarified atmosphere where every lortal thing is taken care of for them. That leads to boredom and frustration, and a need to experiment with ways of alleviating that boredom.
'The devil makes work for idle hands ...' is another phrase that is appropriate here.
I would agree with the point that a lot of musicians and entertainers simultaiously think that creativity is enhanced by drugs, and that they are too smart to become addicted. Both may apply to certain individuals, both may not apply to others.
So - it comes down to opportunity, money, and boredom - a lethal combination as plenty of musicians have discovered, some fatally so.