Because it's a simpler rule to follow than TSA's LGA rule, which is (a) complicated to understand, and (b) arbitrarily enforced.

Ok, it's clear how aerosols relate to food (they don't), and it's clear how liquids relate to food (can't bring your Big Gulp through the checkpoint). It's how to interpret a "gel" that's problematic.

Bringing single-serving sizes of yogurt or apple sauce through a checkpoint can be problematic, if the size of the container exceeds 3.4 fluid ounces. It's even more complicated because such containers are often labeled not by fluid ounces, but by weight ounces (stooooopid Imperial measuring units), and 3.4 ounces by volume may not have anything to do with 3.4 ounces by weight.

On the other hand, bringing a pie through a checkpoint is usually ok, even if the contents of the pie itself resemble a gel (e.g. pumpkin pie). Of course, if you brought a can of pumpkin pie filling to a checkpoint, you'd probably be told that it exceeded the 3.4 ounce limit and wasn't permitted. The inconsistency between those two statements is obvious to just about everyone, yet seems impossible for TSA to solve.

Of course, if you have a medical need for food, you should be able to bring any size item through the checkpoint, subject to additional screening. But experiences shared here show that, often, passengers are forced to defend their medical need for food to TSOs who have little (if any) medical training ... and, ultimately, what the TSO says is what happens, whether or not they're enforcing the rule correctly.

So ... if you can find a way to summarize the preceding four paragraphs in a single sentence, that's great. On the other hand, "don't bring food" is much less accurate, but is much simpler to understand and execute.