Most of the Norway's Western coast (basically the extent of the country) is mountainous so building infrastructure there inevitably involves blasting the rock. At the same time the country is huge, bigger than Germany or the UK. So naturally a lot of tunnels.

This one a bit special: most of the boat traffic through it are meant to be ferries so it is to be commissioned and managed by the National Road Authority. At the same time it's quite unique if only due to enormous cross-section and can't share many usual national design solutions for the tunnels. For instance my company was asked a quotation for a PA system for it and it's really a challenge. So it's no wonder that it's delayed so much: it requires a lot of bespoke solutions.

Need them for trolls to move around.

The Dutch really like building dikes

I bet the cost-benefit is actually negative. But it is kind of cool, I guess.