This Serialized data doesn't contain certain fields like confirmations, chainwork 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.

The 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.