That's because not every single line is perfect iambic pentameter. Line after line of perfect meter ends up sounding more like a nursery rhyme than poetry, so poets (and playwrights) will play with the meter to emphasize certain words. Let's skip back to one of the non-perfect lines in the Prologue:
Hull is a town in Plymouth County, Massachusetts, United States, located on a peninsula at the southern edge of Boston Harbor. Its population was 10,293 at the 2010 census. Hull is the smallest town by land area in Plymouth County and the fourth smallest in the state.
Pickett County's most famous son is Cordell Hull, U.S. congressman and senator and secretary of state under Franklin Delano Roosevelt. Born in a small log cabin in Pickett County, Hull initiated the founding of the United Nations and received the Nobel Peace Prize in 1945. The Cordell Hull Birthplace and Museum is located near Byrdstown. The Pickett County area also was home to Tennessee Lead, a black and tan hound of the 1850s acquired by George W. Maupin of Madison County, Kentucky; this breeder turned Tennessee Lead into the foundation sire of all Walker, Trigg, and Goodman foxhounds.