The other possibility, of course, is that the predisposition that causes some people to want to buy lottery tickets also causes some other behaviour that is more beneficial than the ticket-buying is harmful. Evolution may eventually sort these two out, but changes that subtle can take a long time.
For example, having two copies of the mutation that causes sickle-cell anemia will almost inevitably kill you. But having just one copy of that mutation makes you practically immune to malaria. So in an environment where malaria is sufficiently prevalent the immunity of the lucky is a sufficient advantage to offset their higher proportion of dead children.
The other possibility, of course, is that the predisposition that causes some people to want to buy lottery tickets also causes some other behaviour that is more beneficial than the ticket-buying is harmful. Evolution may eventually sort these two out, but changes that subtle can take a long time.
For example, having two copies of the mutation that causes sickle-cell anemia will almost inevitably kill you. But having just one copy of that mutation makes you practically immune to malaria. So in an environment where malaria is sufficiently prevalent the immunity of the lucky is a sufficient advantage to offset their higher proportion of dead children.