So that is a potential order for 300 a/c. So why didn't Airbus go for it? Now it is too late.
I would think a huge part of the problem would be developing an appropriate engine for a heavy lift helicopter. I don't see anything they can use. The US operates 3 engines you can use in the right power band for the V-22, CH-53 and CH-47 respectively.
The Merlin uses a three pack of motors that are more in the medium helicopter class to be bigger. The CH-47 uses two engines and lifts substantially more. The CH-53 uses three and lifts a lot more.
Europe could either develop an engine, which is expensive, go to a 4 pack design which would be complicated or try to buy off the US. Maybe the US would sell maybe they won't. The only other alternative I see would be to rework the A400m engines to do the job but they have issues already and may or may not be designed as helicopter engines. Who knows how much rework that might take.
So that is my guess. They don't want to foot the bill for an airframe and an engine. The US has pretty much constantly been dumping money into helicopter engines for decades. Among the three references you have two relatively new engines and a derivative of a decades old engine.