That's not a thing. Medical ethics relate to individual patients, so even if you have a coherent public health strategy that makes sense (and a placebo to spread supplies more thinly could be such a strategy), the medics insist on applying ethics to individual patients.

For example the early data for HPV vaccination was enough that as public health policy it made sense to immunise boys. The men would not spread HPV and thus contribute to reduced cancer in any future female partners. But that would be unethical because it's no direct benefit to the boys you're vaccinating. So they waited until they had data showing it would likely also prevent some cancer in men, bingo now it's both ethical and good policy.

Not only are there "enough vaccines to go around", no one is getting placebos and these people have already been working through the pandemic, why would they need a placebo?

Because they are often used to quote something someone said that is probably not true, but you don’t want to take responsibility for it or legitimize it by presenting it as your own word or belief.

Fundamentally, putting a thing in quotes distinguishes between what words you’re standing behind yourself, and what words you’re attributing to someone else.

(there are some other orthogonal uses of quotes, of course, my favourite being when we’re talking about words themselves rather than about the things the words normally signify. For example: My favourite type of animal is dog, but my favourite word is “dog”. The quotes signify that I’m talking about the literal three-letter word “dog”, and not about the type of animal)

In general, people (including people who work for the media) put words or statements in quotes when they’re doubtful of the veracity of those words or statements, and aren’t willing to put their own reputation on the line by making the statement themselves. Instead, they just report that other people say those things.

And so maybe it’s not surprising that a high percentage of stuff which gets communicated to people in that kind of quote structure eventually turns out to be untrue (and often is just laughably untrue on its face).

Since people aren’t stupid and since English is a living language (apologies if you’re a linguistic prescriptivist, but that’s not a fight that can be won), then it probably isn’t surprising that people have learned to associate that syntactic structure with falsehoods.

That’s just how it’s used in the real world. And has been for quite a long time.