Putting a cap on the amount of your cryptocurrency that can be in circulation is a great way to ensure it will never actually be used widespread as a currency. You don't want your coin to be constantly appreciating in value because people won't spend it, they'll speculate on it.

If your dollar was going to be worth more tomorrow than it is today, you're more likely to hold onto it than to exchange it for the goods you wanted. The longer you wait, the more it can get you. Sounds nice for the individual but from a macro perspective, that's a disaster.

When people aren't spending, production is reduced to compensate. In practice this means companies are closing and people are losing their employment, business relationships are deteriorating or being severed altogether. Once the shelves are empty, they don't get filled back up.

Nearly every country in the world uses fiat currency because it can be inflated at will. A little bit of inflation is what allows for economies to be stable.