there is no incentive and it's not in his personality to protect others, it's briefly mentioned but the guy needs magic power in order to use his ability.
green zones were to his complete advantage and there was no clue that if they choose to fight, not to mention together, they would be able to survive. a gathering of well-meaning strangers, it might end up like the last station. it is easier to survive a night in a green zone! big point, the duration of the attack is a wave of monsters with no end in sight, will literally exhaust those with lesser capabilities. even our protagonist who is above average uses a trick to avoid the monsters than face them.
there are conditions to using his ability, it takes time to set up and with the protagonist's persuasion, it is be "best choice" after the green zones were destroyed. there is also the underlying mentality that working together now in this urgent situation, they'll survive