There was Vega shortage for some time, but now it looks better. Huge demand from miners clearly affects it.

AFAICT here in the UK there was a very limited first week release, followed by a restock and since then it's not been an issue.

I am genuinely interested in whether miners are really buying these. Have you any reason to think they are?

I couldn't find much when I looked, beyond speculation about how amazing they might be (but turned out not to be). AFAICT for ethereum you're better off with nVidia 1070s which can cost about 75% as much, have about 75% of the hash rate, and use under 50% of the power.

That's what I've heard from others about the shortage reason. I didn't specifically research mining topic.