Answer:
Andy Warhol called his studio "the factory" because he wanted to recreate a production process similar to the production process that corporations use to make mass products.
The reason is that Andy Warhol wanted to make art that was almost like a product, in other words, pop art.
In his studio, he had an assembly line of silkscreens, and also had many colaborators who were known was the Warhol superstars. These people helped him make the pictures like workers in a factory, hence the name.