At low income levels, taxation is generally low. We've tended to avoid flat income taxes because they impact those with low-incomes more than high-incomes because poor people spend a higher percentage of their money than rich people.

So when you look at how poor people spend money, the rational economist would never advocate spending the money on the lottery. The utility is low, and even if the expected value is positive, the variance makes it a bad idea. Poor people would be better off spending money on things with greater returns.

The problem is that poor people don't spend their money on things with greater returns. They spend far too much of their money on lottery, and it's probably combination of psychological factors and financial illiteracy. I could be off on this, but I remember a statistic showing that there isn't much deviation on how much money any random household spends on the lottery. So a household with $100,000 in incomes spends as much on the lotter as a household with $20,000 in income. The result is that the lottery has become a regressive tax.