Let me rephrase that... more business and cost less than what you're doing now.
It's very simple.
b/c the sauce packets are annoying!
Think about it, when i order a soft shell taco... i have to grab not 1, but at least 2 sauce packets, tear em open unfold the nicely wrapped taco, squirt this sauce into the taco risking a piece of the plastic from the packet getting into my taco, have my taco get cold from this do-it-yourself process, then roll it back up at which point I've exhausted so much unnecessary energy that I'm now pissed at the taco and everybody loses.
but no... instead b/c the sauce packets are at the customers disposal, we just grab handfuls of these packets, like we've just discovered gold, so we leave Taco Bell with 1,000 sauce packets which we're never going to use and eventually these packets just sit around your house until one day you're like "ew the fridge is gross" and you throw them out.
This is wasteful, expensive, dangerous and inconvenient. I think I've made my point.