It don't begrudge Coinbase's handling of bitcoin cash, because it's legitimately expensive to hook a new currency up to their framework, and nobody should be able to force them to do that just by declaring a new currency based on bitcoin.
BUT, everyone should recognize that part of Coinbase's business model is retaining all the privileges associated with holding private keys -- including choices about how to handle spin-offs, secondary services such as account mixing, and so-on.
It's pretty common to derive value from holding on to someone else's cash, so in other products (like bank accounts) some of that value comes back to you as interest, or at least offsets other service fees. Coinbase Asset Management seems to be targeting minimal services, maximum float capture, and maximum fees all at the same time.
determination of value for forks should be made by us. the point is that it's free money, that an exchange could well be pocketing for itself.