I agree it would be to the benefit of every business DT but will brick and mortar restaurants see it that way?
No one is advocating for a food truck to park at a parking meter right outside the door of a restaurant.
If a restaurant business studies the issue, they can find ways to benefit. If a food truck bazaar brings 1,000 people to an area that is otherwise dead of activity on a given night... they will benefit from the increased pedestrian activity in the area. I have personally gone to nearby restaurants for a drink after attending food truck festivals, and that is not an uncommon experience.

If you were a retail business, wouldnt you want all these people walking past your door? Major malls(who have food courts of their own) happily host these festivals b/c they know more people = more sales for their tennants.
Additionally, many brick and mortar restaurants are using food trucks to EXPAND their businesses. Take a look at LA, for example. Many high end restaurants purchase a food truck rig in order to expand their brand and reach customers they normally would not be able to capture in their current locations. Even chain restaurants are using food trucks to expand their reach. Two weeks ago, I walked past a Red Robin food truck in Southern California.
An example of a brick and mortar who is using food trucks to expand their business:


Furthemore, many food trucks will eventually open a brick and morter location after testing the waters of the viability of their concept.
Here are three properietors that started with a food truck on a shoestring budget, and now have fabulous restaurants:


