It's a trick to keep the money for the time being. Many (most?) people don't realise they can get a refund by calling - especially those who do not frequent this forum.

Other airlines are doing this to varying degrees, some worse than others.

It's against all decency. A friend got caught out by it to the tune of a few thousand pounds - now BA say that since he accepted it online he can't have his money back - he's meanwhile out of a job and could do with the money.

Just one more of the usual corporate shenanigans where they hold you to their T&Cs at any cost, but are happy to flout them when it's to their advantage.