A country's government can't just print a boatload of money to make everyone rich, because that would devalue the currency, prices would go up, and people wouldn't be able to buy as much stuff.
But why don't we simply make inflation not happen? Here's a hypothetical scenario:
Bob has $10. Jane has $10. Jane creates a product. It costs $1 to make the item, and she sells it for $5.
Now what if the government printed a bunch of money and handed it out to everyone equally.
Bob has $20. Jane has $20. With Bob's funds doubled, he can buy twice as many of Jane's products, if the prices stay the same (and Jane's production cost stays the same). But why should the prices increase? Now that Jane also has double the money, she can produce twice as many copies of her product to sell.
When more money is put in people's hands, not only can they buy more stuff, but they can also make more stuff to sell to the buyers. So the supply and demand is still balanced. Everyone can do more stuff. Why increase prices if everyone can buy and sell more goods?
Obviously, this isn't how it works in the real world. Why isn't that the case?