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.
I would say the number one benefit to website templates is that they‘re going to save you from having to wait for somebody else to get done with your website. You won‘t control don‘t you? Well website templates allow you to have a personal website set up within a few days after purchasing. All you would need is to select the platform you want and then choose templates that are going to suit it. Now compare this to trying to do everything yourself or hiring a professional web developer. It can take days before the product is even ready to get started.