Is this done or purpose? I see that UnitOfWork is the same (LLBL 2.0).

It means that UnitOfWork2 used thru remoting will loose all collections to save during serialization-deserialization process.

Is there an idea that I'm missing behind this?

That's done on purpose: often a lot of entities in a uow aren't saved or are there only because related entities are saved. When a uow is serialized, the save queues are calculated first, and only those entities are serialized. The rest isn't. This makes using a uow in remoting scenario's much more efficient.

I missed the call to ConstructSaveProcessQueues from serialization Cool.