Because 7 understands all too well what it is to experience a sensory pleasure for the first time. She gets it that the EMH went nuts with the opportunity. She's angry with him, but relates to the experience of existing in one state and suddenly, dramatically being in a completely different state. With your car analogy it would be more like you lend someone your car who has been in prison for 30 years and when they return it to you it is full of the debris of their madness of freedom. And you're pissed off but you also get it.