I messaged them twice at the start of this attack, Whiff saying exactly what you did. While a title remains in the list, someone will look at it, and be tempted to tell them what they think.
I think there is a delay while they do whatever it is they do to ban the poster and label the new thread for deleting, before it gets deleted. If someone has just come on shift and is looking through their emails, there could be another delay.
Getting the programmer to add a filter to automatically zap the obvious troublemakers probably means getting an outside company to do the coding - I have always got the impression that Gransnet itself doesn't have any in-house programmers, they take so long to change anything.
There seems to be a lull at the moment. Perhaps they have applied whatever Mumsnet does.