Same reasons some people like their frontend or backend frameworks to have everything in one place, to have everything in one place.

I prefer to compose libraries that carry exactly the functionality I need, and pipe them together myself. But I'd be a fool if I didn't realize that most people start projects today via some sort of framework that promises (and probably does) a "battery-included" sort of solution, where most of the pieces you'll use have already been put together for you, and you just need to write models, controllers and views (but your framework might call them something else).