Why did the machine politics become common in big cities in the late 19th century?

The political machines of the time became common in most major cities during the Gilded Age for, in my opinion, two main reasons.  First, the cities grew too quickly with immigration and industrialization to be regulated and planned, which invited corruption.  Second, the Gilded Age was tailor made for the rich, who could buy influence and power so that Washington DC would look the other way when they built their machines.

Once built, the bosses relied on rigged elections and the immigrant vote to maintain power and rake in the profits of their organization.