I had a very busy shop in central NY, then we moved south. I opened a smaller shop in TN. Before we signed the lease the landlord said "twenty-thousand cars drive by here a day." During the holidays we were packed, but otherwise we had very few customers. I agree with an above poster, look for wholesale accounts. This can bring in additional revenue and widen your customer base. This helped my overall income but one day we had no customers. No one! I decided to move to a downtown location with a lot of foot traffic. It was a hard decision, I sure didn't feel like packing up an entire business. But it was a wise decision - our average customer count went from 2 to 300.
For now: Do you sell individual items in addition to cakes? For shops with small amount of foot traffic, I suggest filling the case with long shelf-life items such as biscotti, butter cookies, and pre-packaged granola. Customers like to see a full case - the more products you have, the more you will sell. Good luck.
We often have days where no one comes in, most people who do are trying to sell us something instead of the other way around. I think we may have the same problem as you did, foot traffic. Although there are a lot of cars we are on the quieter part f the street and so people don't come as far I think. We have been looking into a store for rent closer up the street where more of the people are. The only other items we sell are cupcake cases and cake boards/drums, sugarflair colours and modelling tools