How does having an async bridge architecture imply that we have to load all native modules up front?

Question

I am trying to understand the fundamentals of how exactly does the new React Native architecture enables lazy loading. It's extensively documented that-

1. The new architecture enables what's called TurboModules that eliminate the need for loading modules upfront.
2. The old async bridge required us to load all native modules upfront.

The above dependencies are not obvious to me. I need help in understanding the following things-

1. How exactly does the old architecture prevent us from lazy loading native modules. Based on my understanding, we only need native module contract information in the JS realm which can in theory be provided by some custom mechanism.
2. If above assertion is true, then it's not really the new architecture that enables lazy loading. Isn't it just an optimisation that we have built along with the new architecture?