Sometimes, it's non-negotiable because there's no money to pay Google-style $300k salaries + benefits.
Fred doesn't make it clear whether he's talking about young startups with very little money in the bank or a mature 8-year old "startup" like Uber that raised $22 billion from investors with $6 billion in revenue. If it's a young 2-person startup that just got a modest $120k investment from YCombinator, a "3rd employee" will not be able to get a $300k salary. The only monetary recruitment tool left is equity.
Fred is also leaving out the game theory aspects of the equity as a deliberate filtering mechanism to attract employees aligned with the founder's vision. Yes, many workers are definitely cynical of startups' self-aggrandizing "we're going to change the world" so they only see one (and only one) way to compensate employees: pure 100% cash and fuck off with your options. An employee certainly has every right to stay rigid to that point of view. However, it still doesn't change the psychology of founders wanting to filter out the candidates with a "mercenary" mindset. They often have no money to pay the mercenaries anyway so they have no choice.