Why is coil whine in electronics so prevalent?

Mostly people don’t care.

When I was a kid I asked adults about that whine from TV sets and none of them knew what I was talking about. The conventional answer was that adults have a hard time hearing the 15khz whine due to age related hearing loss but I am older than my parents were back then and I still hear it just fine on those rare occasions I get near a CRT.

It's because cheap.

It doesn't bother everyone so they can get away with not stabilising the inductors.

The same way they put cheap capacitors with too-low temp ratings in PSUs that burn out prematurely - the consumer just buys a new one so why not.

Especially those remote controlled light bulbs. Why is that a thing? Who wants to have a constant buzzing sound in the background when the light is turned off using the remote.

These days you also have ceramic capacitors that exhibit this same behaviour. Some physically small but high capacitance caps are acoustic noise sources.

> So, I want to know why this doesn't get properly fixed in the manufacturing process. Because nobody cares? Is it too costly? I wouldn't mind paying a small price premium for a product if there was a guarantee of no coil whine.

It is too costly. You want a low frequency to be good at EMC ( i.e. FCC regulations) and you want higher frequency to spare money on components. Easiest is low frequency and hope for the best. Nobody cares about your ears as long as there is no regulation specifying noise. And glueing is expensive and, in the long term, might not bring any improuvment.

Relatedly: why is flickering LEDs so common? I presume most people also just don't see/don't care?

God I wish I knew how to fix them. I can hear all of those, it's a nightmare, I can't sleep if there is one within 10m and no walls in between. It triggers my tinnitus, which then makes sleeping even harder

Two google queries: low frequency transformer whine AND low frequency electronic whine will get you much closer to an answer.

I bought an Intel engineering sample CPU to play with it. It's basically a beta chip they send to motherboard makers. When I enable the E cores it chirps and whistles like a bird, not like the annoying coil whine from a GPU. I think this must be caused by a different phenomenon, but I'm not sure.

Is it too costly?

Very likely.

It's not just the cost of making the the coils quieter, you also have to put them through Quality Control procedures. That's where the expense is.

Then there is also the old adage: "If it works, don't fix it."

Coil whine is merely the modern equivalent of transformer noise.

Most people (especially older folks) can't hear it or don't even notice.

Cost.

Would need an additional 'manual' step during manufacturing, for a small payoff

It's a problem that goes away as you get older, for better or worse.

This is just because You using cheap electronics, for which cost of production is too important.

I have experience in past, with very expensive products, and they where perfectly quiet.

Unfortunately, for some reason, looks like it is global progress slowdown, such compromise-less production near extinct, and each year it is harder to find perfect products.