High yield production needs precise control over lighting, needs to have approx 12-12 hour light/dark lighting for blooming, otherwise it'll grow indefinitely unlike most plants which start blossoming at a certain age. Additionally, having good control over irrigation and nutrients with hydroponics can increase yield. And being indoors is good for security against theft, etc.

Freshness has got nothing to do with it, the product has to be dried in a well ventilated area.

It's generally dried before smoked, or for food products the oil is extracted. I would think the oils would eventually evaporate from the dried or the extract but I don't actually know. It's legal here in WA and the packaging I've seen doesn't have any dates on it so take that with a grain of salt with the supply problems we've had (the state limited the amount produced, so for the first year at least there were reported shortage; they heavily misjudged demand :)).

I'd think it's very similar to tobacco. Vape for tobacco doesn't really expire, it's just the niccotine. And cigs keep for a long time. They get brittle over time, as do cigars, so I would think it's very similar. Again I'm not an expert, I just live in a state where it's common.