Exactly. They likely have power by the hour contracts in place on the 350s in particular, power by the hour was RR's baby and as such they are more heavily exposed than their rivals in the current climate. The 340s are paid off and nobody else will want them so you don't have to worry about resale value by putting more hours and cycles on them. Lufty do all their maintenance in house so will have different economics to consider, eg keeping their engineering teams current etc.
The A343 isn't that thirsty either in comparison to similar vintage widebodies, and certainly more frugal than the other 4 holers still out there.