Photos show the history of the Boeing 737, from the early days to the grounding of the 737 Max

I really enjoyed this article and the level of detail it provided. This part caught my eye, though: "While the initial design featured a T-tail like the 727 with engines mounted on the fuselage, the lead engineer put them on the wings instead, which meant the body could be widened to seat six people across."

Can someone with more knowledge of aeronautical engineering than me explain why tail mounted engines would limit how wide the fuselage can be?