This Serialized data doesn't contain certain fields like
nextblockhash. Is there any reason for this?
Those fields are not actually part of a block and cannot be contained in a block.
The number of confirmations for a block constantly changes as more blocks are found on top of that block. Thus it cannot be part of a block in the serialized data.
The chainwork does not need to be included in a block because it can be dynamically calculated, unlike the other data in a block.
nextblockhash cannot be known at the time of creation for a block because miners can't see the future. The
nextblockhash cannot be known wihtout the current block already existing.