Yes but they gave to their customer 1 BCH for every BTC on balance. But COINBASE not, and it's not a casual exchange, I think it's one of the biggest.
If anybody left BTC on Coinbase at the time of the Bitcoin Cash fork, it's their own fault.
Coinbase sent email warnings to every customer to move their BTC off Coinbase as they would not be supporting Bitcoin Cash.
I got one and promptly moved by coins.
Later some people threatened a class action lawsuit and forced Coinbase to split people's BTC they held in their accounts at the time of fork.
But Coinbase have other priorities so can take their time with that, and are.
Personally i think Coinbase should tell people that expect them to split their coins for them to jump in a lake.
It's your own fault if you left BTC there at the time of the fork.
It's one of the problems with hard forks like Bitcoin Cash, it externalizes the 'costs' onto someone else, in this example Coinbase.