No one is limiting your curiosity; it should be boundless. Don’t lay that on us.
You might as well ask, “Why do I have to breathe oxygen in air? Why can’t I breathe underwater like fish do, as well? Why can’t I fly? Why do I have to feel pain? Why can’t I have everything I want?”
It’s just the way things are. You can be reasonable and adapt yourself to the way things are, or you can be the “unreasonable” person that George Bernard Shaw said has to adapt things to his wants. If you want to adapt things to your wants, then I’d really suggest the flying thing; that would be pretty cool.