I’ve read about and talked to many writers who read mostly in the genre they write in. Actually, most people read primarily in one genre where they find the reading comfortable and enjoyable. They know what to expect.
People should read what they want (although I would challenge them to read different types of stories). I try to read in different genres. I enjoy the diversity of style and form found in stories written for audiences with opposite tastes than mine. Such as romance, horror, and other genres I normally do not seek out and read (nothing racist, dehumanizing, overly violent, etc.). I may not write in these other genres, but I think it helps with my writing.
I feel more capable at providing contrasting viewpoints to my plots and characters. To me, I add depth and strength to what I write after reading a novel outside the genre I’m writing in. As an example, if I’m writing a science fiction story, I read a romance book. How many people know that romance books have happy endings?
This can also be a good technique for grant writers. Sometimes, it’s good to stop writing the proposal and read a horror book. After all, I feel I’m in a horror show when trying to complete a long, detailed grant request.
A creative writer or grant writer should experience reading outside their comfort zone to add variety to what they are trying to write. Sometimes this change can mean publication or funding for a nonprofit.