Contrary to what evolutionists will tell you, I posit that humanity is descended from magpies. If there's one thing that attracts people, that leads them to steal, kill and lie, or to drop everything and jet off on a fool's errand, it's shiny stuff.
Just look at video games - they're absolutely obsessed with gems. Whether it's collecting gems, raiding tombs for gems, or matching lines of gems, precious stones are clearly held up as the ultimate incentive.
Crystal Cave Classic continues this line of reasoning. Here, your sole task is to collect every single jewel from each self-contained level.