Is it bad luck or bad genes that made me develop cushing disease?

Bad luck: Cushing's disease is caused by a growth on your pituitary gland. This disease can occur in anyone. There is one condition called multiple endocrine neoplasia type 1 (men 1) that can be inherited and it causes cushing's disease. This is exceedingly rare so odds are you don't have this.

Not your fault: Quoting dr. Loh:primary cushing's syndrome is the result of an endocrine active mass of adrenal gland cells that become so not as a result of lifestyle habits (good or bad). It's not your fault, but fortunately often completely curable. There are secondary cushing's syndromes related to medications doctors give to treat certain conditions, and it becomes a balance of benefits vs. Risks.