I don't want to spoil White Mage quest line here so read at your own risk.
[Sorry if the hidden text isn't hidden. Never used that code before. =^_^=]
In the WHM quest line in ARR, it is revealed that the Elementals are the trees themselves. When they feel threatened, they summon creatures to defend themselves. It is the job of a Pajal to slay these creatures and soothe the tree. Otherwise the trees just call forth more and more creatures that actually start attacking the tree itself.
[Spoiler End]
So it is kind of easy to see how the Garleans could force their way into the Shroud and also how people could live without catering to their every whim. Centuries of tradition is hard to break though.