Why are there so many books in Suruga Monkey?
That's her massive collection of BL (boys' love) books (which she is also into, besides considering herself a lesbian), at least that's what they represent. As many other things in Monogatari's animation, it should be taken more symbolically than literally. Take for example Senjougahara's "arsenal" of stationery in episode 1 of Bakemonogatari, or even more obviously the constantly shifting, multiplying, growing, falling etc. pile of pencils in episode 6 of Nisemonogatari (you'll know when you get there :) ).