hope...
'bout the only reason i could say, people want/need hope, so they'll cling to anything, even if its illogical... no one in the story is thinking about 'after' they get her X place they're just using it as this week's goal in survival, they've all lived in survival mode so long they most likely aren't thinking two steps ahead unless its in a combative situation... having 'hope' or something to represent it is a bargaining chip, its power, its control... its NOT logical, its not supposed to be because that's human nature...
i've accept long ago that people in stories are idiots, but without that level of innate stupidity events and 'stories' would NOT happen, and while i'd like to think people aren't that dumb 'normally' as some of the protagonists i've seen (who seriously just seem to LACK common sense for the sake of plot .-.) i also know that people are innately stupid, instinct driven, emotional non-logical creatures that will run whichever way they 'think' is right... so yea, waiting out the 'infection' sounds like a GREAT idea, then you realize people are fucking retarded, someone's gonna fuck up and they're gonna be infected and then you're back to square one, ideally having a vaccine could/would prevent the effects of said fuckup... realistically it'd be used to 'cure' the 'chosen ones' and people would fight over it, killing millions, getting more infected, killing those with the ability to actually MAKE the cure, and again, back to square one...
also, have you ever tried using Fire to get rid of fungus? does not work -.- the upper part, the visible 'mushroom' part will probably be destroyed, but the underground part, the actually ALIVE and infectious and evil part would still live one, pop up somewhere else and start all over... fungus is evil, and i was actually very 'happy' about this use in this version of 'Zombie Apokalypse number 253082479t3' because there's a weird sort of logic to it and it IS creepily possible... more so then some crappy retrovirus that 'reanimates' the dead... for all we know fire could make it spread, as the universe likes being a dick, meaning all those moltovs i threw to kill that group of clickers just fucked the world some more XD