I could, and I did for some time, but it's a PITA. The question should be "why should I?". I've since found a Markdown editor that works well for a file this size (Typora - I also had good experiences with Texts).
I've done this in various formats, including single editor, scrivener, and so forth.
I've found that the process of breaking a book up into "chunks" to be a useful one to me. If I can't chunk it, there's probably something wrong with the structure.
But hell, if what you have works for you, go for it. I'm currently using the LeanPub build system which seems to be just enough structure without getting in the way.
Sure, I could edit chapters, or even "acts", separately, and I did for some time; but the novel is a single work, and searching text, replacing text, etc, is much simpler with a single file.
I can see both sides of this. In some ways, this is the old "seat of your pants" vs. "plot the book out" discussion. The important thing is whatever works for you.
Why should you? Perhaps if there are other features of a particular editor that make it worth it. I'm otherwise not one to defend anything that's potentially unnecessarily slow :)