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.
The KCOM Stadium houses Hull City football club and Hull FC rugby club and The Lightstream Stadium rugby club Hull Kingston Rovers. Hull is also home to the English Premier Ice Hockey League Hull Pirates. In 2013, it was announced that Hull would be the 2017 UK City of Culture. In 2015 it was announced that the Ferens Art Gallery will be hosting the prestigious annual art prize, The Turner Prize, in 2017. The prize is held outside London every other year.