I have seen it in teaching. Teachers need xx hours of training per year. Training often satisfies that requirement but provides no significant benefits in terms of pedagogical improvement or content knowledge.
Teachers that want to improve do so by other means. The training keeps us in compliance.
I've known more than a few high school teachers who ended up with Masters or PhD degrees kind of by default via continuing education courses. That would seem to go against your "teachers that want to improve do so by other means" idea, unless I'm confused about the nature of continuing education requirements for teachers.
My assertion is that continuing education credits, or advanced degrees are far from a guarantee of improving a teacher's practice. Continuing education suffers from "box checking." There are a number of reasons for this.
It is in no way a knock on teachers. They are caught up in a bad system and are responding to systemic incentives.
If we apply an always/sometimes/never framework to my assertion, we can find examples where teachers advanced their practice via continuing education. So the teachers you know certainly could have advanced degrees, some even very helpful in improving their practice.
My experience in K-12 as well as studying the history of education reform in America since Sputnik was launched inform this assertion. It has been a recurring theme for 60 years.
We don't gain or lose patients by it; the most recent changes in the field are often so far from settled clinical practice that they're years from anything that would be considered malpractice; we don't get reimbursed better or for it; patients largely can't tell the difference, so it doesn't change your referral stream.
It does little-to-nothing for our careers. We stay up out of pride, and out of commitment for providing our patients with good care.
Medical literature has a pretty low SNR when you look at it from the point of view of "does this help my patients?" Also, PubMed is a thing that's roughly the medical equivalent of Stack Overflow, so you can do some of this "on the fly" to an extent.
They said no career benefits. They don't usually get a promotion for knowing about X or a salary raise so its effects are indirect if they don't actually use it regularly like say a dentist knowing about dental implant options.
Does this surprise you? Interacting with my doctors has never given me the impression that they stay abreast of current literature, and their employment doesn't seem threatened by the deficit.
Keeping abreast of changes in the field and state of the art offer no benefits and is done solely for patients' trust?