Why did the authors of the London Baptist Confession of 1689 callout the pope as being the antichrist?

In chapter 26 paragraph 4 of the 1689 LBC , the authors called the pope the antichrist: >neither can the Pope of Rome in any sense be head thereof, but is that antichrist, that man of sin, and son of perdition, that exalteth himself in the church against Christ, and all that is called God; whom the Lord shall destroy with the brightness of his coming What was the reasoning behind labeling a single man/office as **The** antichrist, when scripture itself does no such thing (and indeed says there will be more than one {1 John 2:18 })?