Hard lines don't burn up with heat round the turbo. If you have ever had a coolant line break near the turbo you know wht it's like. Also oil fires because of a return line cracking do to heat, because it's near the collector is not fun at all.
The wastegates are water cooled also, so having all those lines made with hose makes for a mess under the engine bay. That is the main reason why we built his coolant plumbing this way. No mess, reliable. That is what we are aiming for in his build.
It allows us to make the lines look neat and put lines where hoses would just burn up do to heat. I've seen fire sleeved hoses get brittle over time and leak. Not fun. And it makes one pissed off customer when he is stuck on the side of the highway do to a 5 dollar a foot hose.