The catch seems to be, not cameras themselves, but what you're taking images of. The UAE has some pretty restrictive laws on that front. For instance, pictures of other people
This makes clear that taking a person’s picture without their consent, or in legally permitted circumstances, “shall be an invasion of that person’s privacy or family life.”
“Not only will the camera or device be confiscated and the recordings destroyed, but the photography or videographer may have to pay a fine and be imprisoned. The same punishment is also applicable to anyone who publishes such pictures.”
or military/government buildings
Critical installations, strategic and military locations and government organisations or political buildings cannot be photographed for security reasons.
As a result, it is illegal to capture footage of restricted areas as per the photography laws of the UAE.
That explains this section in the article you linked
[You are] absolutely not allowed to upload anything on social media. This is something you have to keep in mind and no matter how bad the itch. As an extension, you can’t share the footage without the permission from the police, including your insurance provider. Another major don’t is using your dash cam to violate someone else’s privacy – it’s an offense that can land you in serious trouble.
Most likely the police have to review the footage first to ensure nothing illegal is released. As to why there's only one licensed shop who sells them, it probably has to do with all the restrictions around photography (my bet is they have to warn you about the laws).