That's not true about the second driver behind me, because people are not pulling into his gap, because his lane is going 5 mph slower than the other lanes. So he establishes it once and is fine.

This is more of a thought experiment to show that you never have to keep slowing down to zero even if for some reason people continually enter your gap. I barely observe people entering my gap at all in practice, because all lanes are generally going the same speed so there's no benefit to it.