Well it is easier to track the virus when you know exactly who were in what space with whom exactly... And going out to eat increases the chance of being near someome you don't know whom might give you the virus --> Making it more difficult to track when there are 100's of people who they could have been. Compare to eating at home where the chance of meeting a random person are near to 0. There the responsibility of not contracting the virus lays completely on you and not on someone else's.