Because there's no site (that I know of) that organizes books this way so you really can't browse related titles like you used to be able to. In the library shelves, you might find books which were related to what you searched -- even though their titles might not make that obvious.
All library catalogs have a browse function. You can see which books are shelved next to each other, although it is a linear display and you can't just "walk" to the next shelves.
