I believe this debate about the 2nd Amendment became more prevalent in the 20th century because firearms became a business. Hunting, shooting sports, a more advanced military, and police brought on the need for guns to be produced. Companies such as Remington, Winchester, Sig Saur, and Smith and Wesson began to produce guns to meet the demands of the population.
The business of firearms created interests groups such as the NRA, which push for the 2nd Amendment right. They believe it is a right of the citizens to keep and bear arms in order to protect themselves.
The NRA helps to lobby and fund for the Second Amendment. The NRA also supports law makers and candidates, mostly conservative, that believe in the 2nd Amendment. The organization wants this right to stay with the people and in the constitution, which will produce more money.