The first reason would be because hiring a web developer or designer is going to consume far more time than getting website templates. Think about it, you have to explain to the web developer exactly what you want. You have to go over it with them again and again and again. You will have to monitor what is being created and make adjustments during the project. Once the project is finished it is probably going to be behind schedule, and adjustments will need to be made that might cost you more money and more time.
Some disadvantages of prestashop templates are the lack of scalability. The lack of modules makes customizing prestashop more difficult and time consuming. Prestashop also has fewer marketing features than other free e-commerce solutions. End users of prestashop believe the designs to be of poor quality and combine this with the back end being buggy. Many users are frustrated with the templates because of the lack of professional experience in web design industry and especially coding and programming. If you are not sure whether you‘ll cope with the template‘s code feel free to hire a professional to customize the heme for you.