That is planned as an option.i.e the developer decides whether to offer that. Some don't like it because accidental clicks close the sheet/modal which can confuse non tech savvy users.
I think we are well past the curve on the diffusion of innovation chart on this feature. It’s expected behavior that if a modal is focused and the background is blurred that clicking on the background will close the modal (or initiate close).
You can see this for yourself by using a heat-map of your users mouse movement and positioning. Note how many try to close with clicking the background.
Maybe and it will be the default. But since this is a UI kit, I will expose an option to turn it off if the developer prefers that in general or in a specific context.
It'd be nice if clicking the blurred background area on a Sheet closed the sheet like the x button does.