Reasons why this might be true:
1) The "meat" in Jack in the Box tacos doesn't taste as much like meat as it did when I was a kid.
2) Tacos at Jack in the Box cost like half as much as tacos at Taco Bell.
3) Jack in the Box tacos are referred to on the menu as just plain tacos, not 100% beef tacos or anything like that.
4) Occasionally, you hear about someone dying from eating a hamburger from Jack in the Box, but never a taco.
5) Sometimes they give away tacos for free, as a loss leader, whereas, for example, Burger King will only give away fries, or coffee.