They have totally different design goals which is why Bitwarden is more resource-hungry and more complex to deploy. Bitwarden can scale up to large use cases such as companies with hundreds of thousands of employees (it’s what they run on the hosted version, after all), whereas Vaultwarden is designed to be small and light for home use cases where you almost always have <10 users total.
Vaultwarden is not compiled from Bitwarden’s code, it’s a separate project and codebase but designed to be compatible with Bitwarden’s API.
Bitwarden is open source and you can self-host it but IIRC it’s a bit more complex and resource-hungry than Vaultwarden.
They have totally different design goals which is why Bitwarden is more resource-hungry and more complex to deploy. Bitwarden can scale up to large use cases such as companies with hundreds of thousands of employees (it’s what they run on the hosted version, after all), whereas Vaultwarden is designed to be small and light for home use cases where you almost always have <10 users total.