I think, apart from Boult & Woakes, may be Southee as well, rest are not actually proper swing bowlers. Also, most of these players are playing LOs selectively, and they are given rest from an entire series - Amir is been part for every LO squad for last 2 years.
Olden days, fast bowlers mainly focused on Test, and played lot more FC games, these days there are too many white ball cricket, therefore don't think comparison is fair. And, they used similar balls for both Test & ODIs (white color ball), but now they use two different types of balls - hand stitched Test balls & machine stitched Kookaburra. At present the best 2-3 exponents of swinging red ball are Anderson, Broad & Styen - first two hardly plays ODI/List A while Styen's ODI figure is quite ordinary for his legendary status.
Not saying that's the only reason, but may be playing selective series (rather picked for selective series - no point picking in a series and not playing, because he is bowling in nets even if not playing in game) might bring his focus back. Also, when he started, he was bowling with beautiful run-ups & delivery stride, now he is messing up his run-up, bowling too wide from wicket as well. If Left-arm swing bowler doesn't delivery from very close to stick, he is reducing significant % of his chances - won't get LBW much and batsmen can leave lot from the angle. Boult is releasing almost from above the bail and that makes him extremely difficult to leave.