I guess I'm wondering about why they aren't more popular and abundant.
They are popular.
The issue is a legitimate concern to the city. It's not just straight competition.
If food trucks were given free reign, they would impact and potentially hurt the current brick and mortar places. Over time, if some restaurants that are already struggling started closing, it would have a negative effect on property values.
The trucks have a competitive advantage as they have lower operating costs. While they have the advantage, they offer less of a benefit to the city. It would make it less likely for another restaurant to enter the area as the comp. is stacked against them.
It's not as simple as enjoying a slightly cheaper, possibly better tasting meal.