If you think about spread of a virus(and I haven't done the math) Just thinking aloud. It's easy for one person to infect 1 person and 2 people to infect 2 people and 4 people to infect 4 people because of everyday interactions. However, getting 100,000 people to infect 100,000?
That's a much harder nut to crack because those 100,000 infected people will react differently. many will be at home, many will self avoid and then you might be looking at 50,000 or 75,000 having infected having to infect 100k.
So at some point adding new infections would not produce the same "bang for your buck" and rate of spread would naturally slow.
