I tried the food trucks a couple of years ago but ended up paying the same price for 3 tacos as at Hooters and that was without the table, chair, AC, free refills on the drink, and the waitress.
The trucks allow you be able to choose to have tacos...or noodles...or bbq...or pretzels...or cajun...or ten other kinds of foods, all within a one block row, right next to the Con center.
I actually didn't count the number of trucks they would fit into that line. Let's say it was 10 at a time. I just checked googlemaps--going out to one block from the ICC (including just across the street on Illinois) you have 22 restaurants (including Bee coffee and a trio of Starbucks). There may be a couple other Google isn't showing--it's not showing me the Subway in the Hyatt, for example. But let's look at them.
Harry and Izzy
Spoke & Steel
Dick's Last Resort
OP Italian Indy
That's the list of places you won't get into and out of in less than 45 min (optimistically) during normal meal hours. So that leaves 8 that you could get to, eat, and be done with in 45 min. Three of those are Starbucks, one is Bee coffee. So for substantial food, you're down to 4 places.
Now add the food trucks back in, and you're up to 14 places. Even when the lines are long, you are eating and done in 45 in the food truck line.
That is why they are there. No one said the food trucks would be cheaper--that isn't the purpose of having them there. The purpose is to have real food, right next to the Con, and a bunch of variety (not just 10 more ICC food stations), that will be quicker than going and sitting down inside. If you want AC, yeah, go somewhere else. If you want to sit down with a group at a table and chat, the trucks aren't for that either.
And yeah, the quality will vary too. Just like it will with regular restaurants. But the fact that you could go get your tacos right next to the ICC is the reason they are there. Of all the places 1 block from the ICC, maybe a place like the Ram would have tacos on their menu. But the Ram is not in-and-out in 45 minutes. It's an hour, minimum.