I think ultimately it doesn't matter if cartridges cost an extra $1, $5, or $10, compared to the price of discs.
The reality is that most third party publishers don't consider Switch to be a core component of their strategy, especially compared to Xbox, PlayStation, and PC. They see it as a supplemental portion of their business and as such aren't willing to eat the extra cost of carts, which would lead to smaller profits per copy sold.
If companies like THQ Nordic and Rockstar were committed to the Switch long term and felt the platform was a viable part of their business strategy moving forward, they'd price their games similarly to their games on other platforms, in order to cultivate an audience for their games on Switch. Until these companies see Switch as a core part of their business, this will not happen.
I have absolutely no way of proving this, but if Sony launched a Vita 2 with the exact same type of physical media, Rockstar would almost certainly charge $40 for LA Noire on the system, as they'd likely feel more inclined to cultivate a long term audience on the platform and would be willing to eat some of the cost in order to do so. I mean, assuming the Vita 2 was a successful system, of course. Otherwise, they wouldn't bother bringing the game over to begin with.