It's not that the games get ignored, it's that there are hardly any where anyone would predict 1m+ sales before release.
If we use a football analogy here, Nintendo has superstars, commonly sends their best team on the field, plays an offensive tactic and subsequently sees a lot of serious scoring chances of which many result in goals. Meanwhile, we have smaller third parties who have no superstars (i.e. their IPs have never been big), so the best they can do is hang on and get a surprise success here or there, but it's clear that they won't win any league or any cup. Then there are AAA third party publishers who don't want to field their best team and play an incredibly defensive tactic, simply because they don't play with the attitude to win, but rather the attitude not to lose; unsurprisingly, if you have next to no scoring chances, you can't score many goals. This is very basic stuff.
So if you look at a bestseller chart that is naturally very top-heavy, Nintendo logically has a much stronger presence than third parties because Nintendo puts in a lot more effort. That can't even be argued, because it's so blatantly obvious that Nintendo is the best publisher on Switch by a huge margin.
The OP also puts the cart before the horse. The premise is that third party games get shunned, but what precedes that is that third parties shun the Switch. Third parties have to deliver the goods if they want sales, because gamers have the choice to put their money towards better games. We have yet to see third parties bring big titles to Switch without falling short in areas like time of release, price, marketing, quality, or even making the whole game physical.