Because of the oft-repeated claim (including in, yes, TMND) that "ordinary" households can accumulate extra-ordinary nest eggs. It's no contest, I just like to see claims backed up by evidence. Blame it on my scientific education.
Ordinary to me means near median income households without significant luck (i.e. early employee of Google).
It has been many years since I read it, but as I recall TMND, they spoke about playing good offense (making money) as well as good defense (not spending money). They wrote that a fair number of people make sufficient money to become a millionaire, but they piss it away on buying stuff that they do not really need. As I recall, they really emphasized that "acting rich" was often a huge barrier to actually being rich. The one thing I do not recall is the authors saying that everyone, or even most people, could become millionaires. And I have never gotten the impression that people on this board believe that anyone, no matter what their income, can become a millionaire either.
I suppose you're entitled to construct whatever strawmen you want, but you shouldn't be surprised when others decline the opportunity to help you tear them down.
EDIT TO ADD:
Upon reflection, I think you're entitled to a better answer than that. So let's approach it this way. The Census Bureau says that the median household income in 2013 was $51,939 (source --
http://www.census.gov/content/dam/Census/library/publications/2014/demo/p60-249.pdf). Now, let's assume that the household really buckles down and saves 10% of their income, which would be savings of approximately $5194 per year or $433 per month. Let's assume that they earn a 4%
real return on their investments. Using this calculator
http://www.interestcalculator.org/savings.php we see that after 40 years (say, ages 22-62) of saving, they will have amassed only $511,789. They would either need to save 20% of their income to become millionaires, or earn 6.6% in real returns to amass a million, or some combination of greater savings and higher return (15% savings and 5.1% real return would work). It would indeed be difficult, but maybe possible for a few.