Good writers read. That’s pretty much a given. Good writing incorporates elements of multiple genres. If a horror novel was only horrifying things happening and no suspense or romance you just get horrific events happening one after another. If all you read is science fiction you don’t gain knowledge of other elements. There are happy books and sad books. Books that teach you about creating endings that pull at the heart of your readers. Books that make you feel like a warrior or inspire you through the journey of the characters. There are so many ways to tell a story that you could spend a lifetime in a genre and never experience the focus of other genres. Taking in a variety expands your mind and exercises your imagination.
It’s like exercising a new muscle group. You might have great disdain for romance or horror but one day find yourself drawing on elements of those genres to better express stories of your own.