if we do not know the reasons these frontline workers chose to let someone else take the vaccine, rather than take it themselves.

My own personal estimate is that the majority don't want to be guinea pigs (that's mentioned in the article, many people don't want to be first) although it's quite possible some believe the need is else where. Or both, they're not mutually exclusive.

My wife didn't volunteer to be one of the preferential first. It wasn't like an order or anything people declined but rather you had the option if you wanted it. The expectation was, also mentioned in the article, there'd be more takers than vaccines.

To be fair to the article, the relevant info is there, it's just propagandized to support a certain narrative.