Difficult to root is an auxin sensitivity case. This could(!) be affected by many factors. I would personally give it a shot no matter what people say. If you find the one auxin-sensitive and easy rooting mutant, you've struck gold: people will want to buy loads of those cuttings because it means those people could reproduce them by the thousands.
This mutation can be base genetic (from seed) or epigenetic (through "experience" or external factors).
If they prove to be hard to root, it might be effective to throw in some cytokinins like 6BAP, zeatin or kinetin. At a +/- 5:2 ratio of auxin:cytokinin. Sometimes this flips a switch to which plants respond with good rooting ability.
If poor rooting is caused by phenolic bleeding (darkish stuff leaking from wounds killing the cutting) then vitamin C and/or activated charcoal could fix phenole-induced inhibition.
Even if you're not going for it, it might help someone else who wants to figure this out.
