Larger block sizes require more bandwidth. It sounds logical to just increase the block size. However, bandwidth doesn't follow Moore's law. It would create an imbalance in access to mining. Also larger block sizes will favor minors that have mined the most recent blocks. Especially in China where the Great Fire Wall will make it so that by the time your last block is in sync, they are already mining the next block.

Segwit takes all the input signatures that are redundantly processed over and over again on the main chain and sets them aside since the signature has already been hashed. This makes the data size of the block much smaller which means miner fees are smaller, until the 1mb is filled.

bcc was announced by VIA BTC.

Segwit arrived through consensus.

Which one is Bitcoin?