Yes, it's still a lot and there are ways to sell the stock but that's assuming they even get $20 million.
If you are earning $40k - $60k/year - which many young founders were likely earning before joining YC - even if after multiple dilutive rounds of financing you end up with 10% of the company, in a $20M exit....that's still $2M.
Sure, you can't buy Fiji....but you are literally going from a bank account with a few hundred/thousand/tens of thousands, to literally hundreds of thousands/millions.
That is VERY major the first time it happens.
I guess the point I am making is, the jump from having $10K in the bank to $1M in the bank, is SOOOO much bigger than from $1M to $100M - because it impacts your life much more.