Because human activities are error-prone, evacuations cause an increase in fatalities; so any evacuation decision has to be balanced against the risks of sheltering locally.
Evacuations cause fatalities; both directly, by decreasing compliance with future evacuations (as happens if the situation turns out to be not as dire as advertised), and by hindering even more necessary evacuations in nearby areas.
Non of this is relevant to this case; lack of money shouldn't be the reason people don't evacuate. If the government determines that evacuation is warranted, it should fund an evacutation. (Of course, this policy could backfire if it means the government calling for fewer evacuations).
Compared to what, not evacuating and having hundreds of thousands (or millions) weather out a major hurricane? That seems doubtful..