They still had a license for it and it was tech they knew and understood well. The EOL may have occurred in terms of sales, but Autodesk still supported the license and so it makes sense for a small studio taking a big risk on a new product to reuse what they can.

Have you thought about reaching out to them and offering to show them how it can be optimized? The number of SWE's out there that understand GPU architecture and game engine optimization for DX[11-12]/Vulkan are a select group so if you can lend any help here I'm sure they'd greatly appreciate your expertise.