I know one of the benefits of having a PU component is in the lamination and taping processes. Because PU adheres so well to the adhesive, Gore most likely thinks that the sacrifice in breathability is made up for in its durability.
Actually, I'm not sure this is the exact argument Gore uses. Don't forget that first generation Gore-tex had no PU-layer (and thus was even more breathable than eVENT). Even now almost 30 years later, the only argument I've heard why they added the PU-layers was the contamination issue. What I have heard is that Gore assumes or assumed that the inner coating is/was not durable enough and that in the medium or long term, contamination of the PTFE membrane could still take place. But to my knowledge, the enhanced production method used by BHA should address part of this problem. OTOH, even if contaminants would physically start to block the pores of the eVENT membrane, it would be much easier to remove than in first generation gore-tex since the bonding strength of the contaminants with the membrane woulde be lower in case of eVENT.
Even if the lack of a PU layer makes the construction harder and thus more difficult, then I still can't see why Gore wouldn't investigate this route. Can you imagine that a brand like Arc'teryx wouldn't jump on this wagon. They praise themself as the masters of lamination technology. Look at their line of packs or the new climbing harnesses; lamination is a distinct feature of all those products. I can 't imagine that they would leave this challenge to others. So what if it is more expensive. Since when has the price been an issue for Arc'teryx?