For readers, this is an easy answer — because no matter how much you like a genre, it gets old after awhile. Everything starts to seem exactly the same, and if you read one more book about mermaids, you’re going to tear your hair out. So mixing things up keeps reading fun.
Now, for writers, we know why we need to read IN our genre — it teaches us the genre conventions and tropes. All genres have them, the things that define the genre in the readers’ head, the things they expect.
But why read outside of it? If you’re writing fantasy, how does reading mystery help you?
The best stories are the ones that resonate with people, and to do that, you need to understand people. A lot of that comes from life, but a lot of it also comes from the media we consume. Reading outside your genre broadens your horizons, which can never be a bad thing.
Aside from that, there are things to be learned from every genre. Thrillers can teach you how to up the stakes and keep your readers hanging on every word. Mysteries teach you how to mix in foreshadowing and false trails. Romances teach you how people relate to one another (and how to write a proper sex scene – I swear, everyone feels like they have to stick them in now, regardless of genre or story, and a lot of people shouldn’t…). There’s little tricks to be learned everywhere.
Plus, you can tie this back in with why readers read a variety of genres–if you always read the same thing, your writing tends to follow what you know, resulting in just more of the same. Innovation comes from trying new things and new combinations.
So don’t sell yourselves short, Squiders. Go out and read with abandon.