This quote from the article seems to answer your question fairly well.
> No one has ever done anything great in EVE without someone else wanting to destroy it.
> 600 billion ISK in resources spent to destroy a station
It's not like they lost that money. Unlike cars, internet spaceships retain their full value after leaving the lot. They can just sell those battleships back or keep them around as part of the fleet.
The primary motivation is that players' understanding of the current meta suggested an attack like this was impossible.
This is the kind of thing CCP puts up in-game memorials for.
Some men just want to watch the world burn.
The write-up says this operation was quite costly - 600 billion ISK in resources spent to destroy a station that cost "hundreds of billions of ISK" in the first place. Did the Initiative gain in-game resources and advantages that were worth this costs, or was it mostly just done for the challenge of doing something no one thought possible, and proving their might?