There is a few reasons really…
Because they mix in batches with a scent and unscented is a custom addition even though your not adding anything. It takes time and other resources for them to go back and remix dry mones to create unscented.
For pheromones to work you need to bind them to a scent which then diffuses off the body into the air. The binding agents and fixatives are in the scent package. The scent is what carriers the pheromone. Now it is possible to mix unscented mones in another scent and achieve some degree of binding but if you dont know what your doing its not always effective resulting in complaints and returns.
The reason they use neroli is because it blends with just about any scent. So it can be used both on its own or be covered with another scent and blend well if you choose to. Most high end colognes use neroli in there mixes for this reason.
If the scent bothers you then I suggest getting the light neroli option so you have the binders with less scent.
Harris explains a little on this subject here >>>>>>>>>>
Tisha