How come I have easy bruising, but nobody else in the family has it?

No simple answers. You may have developed easy bruising lately because of some changes in your body. You may have inherited the tendency, but no one other than you in the family may have inherited it.
Possible New mutatio. Get your complete blood count and pt/ptt/inr checked if you have'nt done that already. Easy bruising can be suggestive of low platelets. It is not necessarily a genetically transmitted disease.