Why do most people not recognize a loaded question? First, let's define a loaded question: it is a question that contains a controversial or unjustified assumption. These kinds of questions are quite successful at getting people to accept information with which they might otherwise not agree.
Back to the question. One possibility is that attention is diverted from accepting the claim stated in the question to answering the question. This diversion can be mitigated by simply being aware of the loaded question and looking out for it.
Here are a few examples:
1) Why are sitcoms so trashy these days? Sitcoms might be trashy by someone's standard, but this is still an unjustified assumption.
2) Who is the "banger" of the Big Bang? Who said there has to be a "banger", and why does a "banger" have to be a "who"?
3) Why do most people not recognize a loaded question? Did I get you? A claim like that should have a reference; given the kind of study that would have to be conducted to provide evidence for "most people," it would be safe to assume that this claim is more rhetorical than factual.