It is also worth understanding when you situation is far more stable than most people. If you've got a stable job and considerable assets then you can basically self insure. Yes, if you surprise need $40,000 and the market is down it will suck to sell a bunch of investments from your taxable brokerage account or rapidly get a HELOC but that case is rare enough that you are willing to eat the loss in that case for additional expected growth.
Almost nobody has this. The r/personalfinance memes exist largely as "the very basics for people who don't have the first idea how to plan for their financial future."
This is just another one of those benefits of being wealthy. On average, self-insuring saves money. But for a lot of people an emergency fund is a critical thing because they don't have access to liquid assets without gargantuan 401k penalties.