Like Global Warming, this “solution” was accepted because it supported the overall agenda.
The agenda in this case is to discourage oceanfront development, tourism and use by humans of the shorline. The shorline is to be preserved for wildlife and the very few humans wealthy or priviledged enough to partake of the rare beauty. So knocking down condos and kicking the hoi-polloi of the beach in order to plant mangrove trees has very little to do with Tsumanis.
Similarly with Global Warming, the agenda is to discorage American consumerism and energy consumption. The best way to do that is to make energy scarce and expensive. The best way to do that is with a carbon tax.
trees would just add to the debris coming at the victims.