Exchanges have to consolidate every single input at one point, and when you look at what happens with your deposit, it's usually sent back and forth, which all cost them unnecessarily more in fees than when they would have Segwit fully adopted.
Your words are true, but this requires modification of the entire code on the platform, note the amount of damage that may occur when such vulnerabilities occur.
Many newbies wallets still don't support bc1 addresses, so you'll find that people using these addresses is less than the benefits from them.
Generally, as adoption increases, they will have to update the code in the future.
First blockchain.com and now Bitfinex too. Coincidence? It could be that they are trying to get ahead of the game as blockchain.com has launched an exchange not that long ago? Thanks for the heads up.
Note that BCH/Altcoins supporters do not want to see low Bitcoin fees.