Did you see the line between 0 and 1e7 (again, your notation is flawed)? That's also from your data... an it's linear down there, too. Everything says it's linear. Why do you think differently?

it's linear. There isn't a limit. Using the same code, change the input x data to as many points as you want, going from 1e5 to 1e7, distributed however you want. You will see it makes a straight line. There is no discontinuity, there is no limit. If you counted at one per second, it would take you a million seconds to count to a million, and a billion seconds to count to a billion. On a different scale, that's what is happening here (since CPU counts faster than you).