Because, while it's a perfectly valid argument to make, technically winning an argument is different to actually winning an argument.
If most people don't know what a logical fallacy is, then you may as well be referring to the argument from magic pixies and fairy dust fallacy: they won't care or understand what you're saying. At worst, they'll assume you have an unwelcome air superiority about you and they'll start to ignore everything else you say as well.
The sad fact is that people listen to emotions because they can relate to them and, however invalid such an argument is, it's often the argument that wins.
