You see, if you only sell one product, you need to find those prospective customers that want that one product. Add a second product, and you've opened the door to customers who want it, but not your first product. Add a third, and you have more prospects, and so on. That way, your customer can see all you have to offer in one place, instead of one ad here, another there. Having a catalog will increase the orders you receive, since your customers have more choices and you can show them everything in one mailing.
Catalogs are expensive.
If you're thinking of putting together even an eight page catalog, call your local printer and ask for a price. Get a quote on 1,000, since you'll want to have enough. Then, you have the mailing cost, which would be 52 cents. You're now up to 67 cents per catalog. Add in the cost of getting the name to send the catalog to, and you could be over a dollar per catalog.