GM is a huge outfit, so a recall could involve a large number of cars simply because they sell a large number of cars. But the number of cars recalled, while astronomical, isn't the real issue. The real issue is..
A: How widespread and pervasive the problems are throughout the entire corporation, from air bags to transmissions to windshied wipers to ignition switches to faulty shocks...and a whole lot more, spread throughout several GM divisions and dozens of different models, not just one car or one division. The faulty parts and problems are everywhere.
B: The even larger problem is that GM knew of some of these defects, yet did nothing about it for years. They just kept cranking out faulty cars, and they knew it. And they tried to silence any whistleblowers who brought up the problems.