The flying is actually easier, the 787 is so automated it in every respect that anyone could transition from say a 73 with little fuss.
The flight management on the other hand is completely different. We have lots of guys moving from short haul flying where a suitable diversion is never more than a few minutes away to long haul flying where the only alternate is 2 hours away and guess what.... it's now 25 knots across in a snow storm oh and there's unlikely to be any hotels available for the punters!!
I'm not saying that it's particularly difficult however, the training required is different and maybe some operators just don't have the capacity for extended ETOPS courses when they can just recruit experienced guys from day one.
Cheers