It is because democrats dont care if gang members and organized crime have machine guns. They only want law abiding Americans to be defenseless against democrats when they get totalitarian rule and can send the army after anyone that does not agree with their facist communist ideology.
Obama admin did not sell the machine guns to Mexican Drug Lords the Obama admin gave the machine guns which were bought with taxpayer money and given to the Mexican Drug Lords. Obama admin borrowed money from China to buy machine guns to give to Mexican drug lords and taxpayers are left to pay back the loan with interest. The Mexican drug lords promptly used the machine guns Obama gave them to kill border patrol agents and US citizens.
Obviously Obama and demoncrats dont care if criminals have machine guns. They only want to disarm law abiding citizens so that Obama can be a dictator like North Korea dictator and rule Americans with an Iron Fist.
Democrats also want to violate the 2nd Amendment by trying to pass laws that infringe on the rights of gun ownership. The 2nd Amendment says "the right of the people to keep and bear Arms, shall not be infringed."