Why Segwit makes blockchain faster?
First of all, your understanding of segwit is incorrect. There is not extended block, the witness data is still part of the transaction.

Segwit also does not "make the blockchain faster". What part of it does is it redefines the maximum block size metric to be something called block weight. Witness data is weighted differently from non-witness data, which means that a block containing witness data will have more spare weight units to contain more transactions. This means that Bitcoin's transaction capacity will increase, as will the size of blocks.