Yes, all these people could probably make different choices to save a bit more money, but a) min-maxing life like that sucks, and b) most people constantly giving this advice didn't do that themselves. Is there a single person in America who:
1. At 17 years old ignored every single adult in their life and wisely chose to go to trade school instead of college because their 30-year projections of their own life showed loans might be too much of a burden
2. Stifled all personal ambition and passion and chose a career with the most objective earning potential
3. Cut off all friendships and moved to the lowest cost-of-living area where they could still find a job
4. Lived like an ascetic hermit until they had a large enough emergency fund in the bank
The answer is no, this person does not exist, if they did they would be miserable, and nobody wants to live in a world where this lifestyle is necessary for an average person to feel financially comfortable.
Edit: Also, when you describe $40,000 as a "low income", are you aware that the median income for a 20-24 year old is less than that?