It is said that there was once a great king in Sinnoh whose ambition could never be satiated. Although he had inherited a vast kingdom, he saw the riches of the rest of the world, and became overcome with greed. He taxed his people into poverty and waged constant warfare, building a vast empire but leaving his people in ruins. But when marching his army south to invade Almia, this king saw a Shaymin, and wept in gratitude for everything he had been given, from the loyalty to his men to the wealth of his treasury; only then was he finally satisfied.
Some say the worshipers of Shaymin are still grateful for this particular incident, for by swaying a king's heart it had saved a generation from tyranny. But Shaymin itself has the power to induce gratitude, and there are reports of it being thanked for fine harvests and peaceful days long before this king reached the throne. And this story of the King of Sinnoh has been echoed time and time again – from cruel monopolists to great pokemon trainers who treated their pokemon as tools, people in every era have been inspired to change after witnessing a Shaymin and thanked that pokemon for everything they had.
And there is much to thank Shaymin for. This era is one of peace and prosperity, where people have ample food, no war, and the freedom to pursue their dreams. It is, to be sure, usually a dream of pokemon mastery, but there are many other things people strive for in life. It is perhaps excessive to credit all anyone has to Shaymin, but there is something to be said for a god that is not begged for miracles, but thanked for one's own happiness.