Why would this be?
There could be a few reasons, possibly ad targeting, the target market had little or no disposable income, perhaps there was no secondary monetization or a few other things. Most good video marketers would agree though that purely based on ad revenue, making a decent amount of money solely via video creation could be a hit or miss affair.
How could things be improved?
The first thing would be definitely not to rely on ad revenue alone. Even an Amazon affiliate link to a related product or a CPA (Cash Per Action) offer – where someone clicks through a link to a site, enters simple (usually) non-personal detail can generate a few cents to a couple of dollars would probably improve the income no end. Offers around affiliate themes like these abound throughout the internet and far from being a scam way of marketing, they are merely an extension of commission based sales that have been familiar in the retail world since it began. These links would be placed in the description box or even in the comments section. Anywhere where they might attract attention.
Talking of attracting attention, that is something that definitely should be done. At least 3 times in a video and perhaps more if it is longer than average – At the beginning, the middle and at the end, even if only by a text message across the bottom of the screen although it's better if mentioned by the presenter. With YouTube's own caption system, these messages can even be live links, making it very easy for the viewer to become a prospect or a customer. It just needs to be said somewhere, that a live link is present to something helpful or valuable for the viewer.
This mention, otherwise known as the 'Call To Action' is so often missing, not only from videos but in many other forms of sales advertising. You don't quite assume the reader or viewer is so dumb that they don't know what to do. They just need reminding sometimes and require a push in the right direction.
From a long-term point of view, it is much better that a viewer becomes an email subscriber. Yes, YouTube has its own system, but it only nudges a return viewer in the direction of a producer's new video, whereas an email subscriber could be pointed directly to a new production, hence it could be a good idea to encourage viewers towards an email squeeze page, where a reward or gift is offered in return for their email address. This usually means buying the service of an autoresponder or mail management company but does mean that repeat viewers can be contacted and given more details as and when the producer sees a need and not just when a viewer happens to go past YouTube again.
So the answer is 'Yes', it is possible to make money from YouTube, but it won't be the sporadic drips and drabs of the sometimes random ad system.