Help me here. What good is crypto stablecoin if there has to be $1 for each dollar created? Why not just use the dollar?

Because the dollar is not native to a blockchain. Therefore, the dollar can't directly be used inside of the blockchain system.

Crypto can be a bit opaque, and for a good explainer I highly recommend Matt Levine's lengthy piece on it (you might already have read it, link below), but in a nutshell crypto is basically a system for moving around entries on a computer ledger. That happens in the "normie" financial system as well - most financial transactions don't involve moving actual dollars or other assets around, but instead also involve moving entries in a computer ledger. These entries represent the assets. In crypto, these entries are the asset, which can be used to buy other entries/assets that are native to that blockchain.

A flawed but useful model would be to think of the in-game currency for any role-playing video game that you've ever played, such as gold that you might find in a game like World of Warcraft. Each of those "gold" units that exists within the game world can be used to buy other things that exist within the game world. There's typically no direct way to use real-world dollars in the game world economy, or vice-versa - the online currency has to be exchanged for real-world dollars (or the reverse).

Stablecoins are useful because they are native to a blockchain, and therefore can be the direct subject of blockchain operations in a way that dollars cannot. Blockchain fans believe that this will be enormously useful, because blockchain operations can be decentralized and trustless in a way that conventional transactions cannot be. I'm skeptical of that supposition, but that's the reason.

bloomberg.com - The crypto story