[yathrowaway2]

It's all about marketing.

Doge is a fork of Bitcoin, but not actually very interesting as a cryptocurrency (e.g.: https://github.com/dogecoin/dogecoin/issues/1674). It's the "fork the codebase" approach that vimy's comment mentions.

Newer currencies generally don't fork the codebase of an existing one. Shiba Inu is an Ethereum smart contract (ERC-20).

Interesting places to start reading are about smart contracts (ERC-20 on Ethereum), parachains (on Polkadot) and also just browsing around coinmarketcap.com (e.g. you can find security reviews of various contracts, which can be very interesting reading).