It is fairly simple to create one, you can do it in a few hours. There is an open-source ABI compatible to AB's implementation available here: https://github.com/kepmehz/ScriptHookRDR2V2
However, since AB usually updates his hook fairly timely, why create another one that does the exact same thing? That is not a great motivation for most developers. The one I linked was born mostly due to uncertainty about AB's situation, but generally speaking keep in mind people here do this for free and for fun and recreating something is usually not that fun. Especially when it is not abandoned but just takes a little longer to get updated.