The explosive population growth of the late 18th century provided both the supply and the demand that fueled the Industrial Revolution. As living conditions improved, infant mortality decreased and life expectancy increased. Having to feed and clothe significantly more people than before meant that the farming and manufacturing processes in place needed to evolve to meet these new demands.
The Industrial Revolution may never have begun if it had not been for the attendant rise in population. Farming and industry had been very unorganized and inefficient but were still sufficient to meet the basic needs of the people dependent upon them. With life expectancy so short, little thought was given to such ideals as "quality of life." People barely survived, but civilization limped along.
As more children survived to adulthood, and then more adults lived longer still, more food and higher quality goods were required. Inventions that automated farming and manufacturing processes were implemented. Previously, demand had not been high enough for people to change from the methods they were accustomed to. As supply began to fall short, people looked for more effective means of production.
Having too many people for one farm, town or village to support created a surplus of labor. That labor was put to use in the towns and cities that built up around the new factories.