a template is a basic form. Someone has to adapt it. It's like the question why do we need cooks if there are recipes.
Well ofc you can do it yourself, but as everyone who ever cooked finds out. It takes time, it's not always as easy as we like to think and we have to clean up afterwards.
That's why some people just like to order food becauce they have someone who cooks for a living.
That's why people need web developers. It's like every other job, it's easy on the surface but it's still work.