Printing more of a currency causes inflation, or basically the more of a currency, the less valuable it becomes. Think of diamonds -- if there was only 1 diamond in the world, it would probably be worth more than anything else in the world. But now if there were enough diamonds in the world for every person on earth and their ancestor and their descendants, probably not going to be worth as much.
Yes that's why we can't just print it again and again like without limitations. When I was a kid, I'm thinking about this out of my imagination I didn't know that this will cause a big problem to the economy of a country. And even in local currencies, they can't just keep on printing their paper money because it will affect a lot of businesses. And that's why it's good to have bitcoin that has 21 Million supply limit.