Native ads is great when you have volume. Hes struggling because its a micro niche site, which means,
- Small amount of content targeting a single topic (hence, micro).
- Small amount of traffic from main keywords/longtails usually amounting to few thousand searches tops.
But maybe native ads would perform great if its targeted, not mostly viral crap or get rich quick shit.
You didn't give more information for us to properly advise you. Sadly, in 2019 micro niche sites are not favoured as it used to be years ago. Also, a micro niche site is no good for display ads in general, unless you build a lot of them which will amount to enough traffic and thus, you get a fair amount of revenue. Best scenario is finding a Product to promote or try
Buysellads and similar marketplaces to find laser targeted niche advertiser(s) which will appreciate your site more than you think