This is the area which really seems to cause some trouble for people when they first start playing the game. In order to sell your product, you have to get it on the shelves. Your salesmen are responsible for getting your product on the shelves in regions in which you place them and in regions surrounding those regions. If, for example, you don't have a salesman or site in Europe, you can't sell any product in Europe. If you move a salesman into Europe he will make your product available and people may start buying it.
Availability is the first important factor.
After that there is demand, which is determined by price, attractiveness to the given market and miscellaneous bonuses, another area which seems to escape new players. Much of your product demand depends on market momentum. Of course not, but Gateway has market momentum. People buy their product because they are familiar with it, and for another product to make a dent in Gateway's market share it has to not only be better than Gateway's, it has to be significantly better. It also has to have some marketing to give it a boost and probably a better price.