In conversations with folks in the biz, a typical expectation for conversions of "expressions of interest" to actual purchase is around 50%. Before the creation of the RegA+ process when only accredited investors could play, requesting a prospectus would have been considered an expression of interest, for example. So "allowing" $50mio in expressions of interest makes sense when your fund-raising target is $25mio. Conversely, when the new process only allows for a maximum solicitation of $50mio, it is prudent to say you're only looking for $25mio.
Remember that this process added another wrinkle never seen before - you HAD TO express an interest to get a place in line to purchase shares if/when they became available. Deciding later to invest would do you no good if you didn't have a place in line, and that likely created a sense of urgency that drove many placeholders, knowing that you could decide later - without penalty - to not invest. So.......likely penalty if you don't decide now, no penalty whatsoever if you hedge your bets and decide later. Simple decision.
I don't think it's reasonable at all to use the word failure to describe the results here. In fact, I think the word disappointing can only be used in the sense that "I'm disappointed that production dates have slipped" when my gut expectations from the beginning were that a project of this complexity had/has a much higher likelihood of schedules slipping than not.
This RegA+ is an entirely new process, and the industry will undoubtedly use this experience to start building new expectations. I'd be willing to bet the 50% expectation gets revised downward for the next fundraiser of similar magnitude.