Cubdriver suggested some good books. I found the following in, "Airplane Design: Part II, Preliminary Configuration Design and Integration of the Propulsion System".
On page 110 is a table of historical data on fineness ratio based on category of aircraft. The Jet Transport category shows a fineness ratio (Length Fuselage/Diameter Fuselage) of 6.8 - 11.5.
The Roskam series is based on using empirical data from past aircraft to do preliminary design of new aircraft. These cited numbers include a huge range so it might not help much.
I think the Anderson book will teach you more about the fundamental physics but it will have some serious math. One contribution to total drag is a function of the surface area (aka wetted area). By playing with some geometry, you will see that adding length to a fuselage will not increase the interior volume as efficiently as increasing the diameter of the fuselage with respect to wetted area. However, the surface area when viewed from the front is a competing factor that also contributes to drag. Part of the problem is in optimizing this fineness ratio. This is very simplified and there are other complexities to incorporate as the speed increases into the transonic regime.
As Awax explained about the growth of the 737, sometimes the reason for a design decision isn’t really based on optimizing the physics. It could be that a decision is based on financial constraints or the need to incorporate existing technology. For example, the super long 737 allows airlines have one group of pilots with common “type rating” fly a larger variety of aircraft. An engineer would probably never design the 737-900 if it were a “clean sheet” design. It only makes sense when you include the financial, regulatory, historical environment.