It's not a small significance, and it's not FUD. It's admittedly possible to take some measured numbers for the prevalence of one of the nitrosamines, put that through a dose-response model (of controversial accuracy) and come up with low-sounding numbers of expected cancers, but that's not enough to dismiss the issue.
Nitrosamines are notorious carcinogens, the side-reactions that produced them is well-known (if this comment (https://blogs.sciencemag.org/pipeline/archives/2019/01/04/th...) is to be believed, known since the 1930s), and detecting these genotoxic impurities is feasible without exotic analytical equipment.
The mechanics of the synthesis routes should never have allowed production of those impurities, the active pharmaceutical ingredient should have been monitored for these impurities as well, and this aberration should have been discovered far earlier than it actually was.
It's a lot like foreign object debris in aircraft, or retained surgical instruments inside a patient. Neither are a guaranteed death sentence, but they're harmful, utterly avoidable, and their prevalence is a good indicator of careless/inappropriate working practices and inadequate monitoring procedures. If their procedures couldn't detect these nitrosamines for years -- what else is being let through? Heavy metals? Pyrogens? Some other class of toxic chemicals? Inadequate/overly-high active ingredient dose/concentration?
I've installed avionics inside other people's aircraft and I was careful to not leave behind any tools / bits of wire insulation / snipped-off wires / screws / etc floating around. Yes, the probability that a single bit of wire will find its way onto uninsulated connectors is small, but that argument is not an excuse for sloppy working methods. With life-critical systems, it's not OK to be careless just because someone else might catch the problem or because there's other subsystems that'll attenuate the severity of the fault.