Games sizes are getting huge, and we're getting to a point where it's not financially feasible to include an entire game on multiple discs anymore. Thats likely the large chunk of the reason why, pressing millions of triple layer discs or even multiple single/dual layer discs is way too expensive when you can just plop part of the data on a significantly cheaper single layer disc and let users download the rest from servers.
You mention RDR2, so I'll use that as an example. The games data, in total, is 99gb when all said and done and installed on a PS4. Which means it would either require 4 single layer Blu-ray discs, or two dual layer Blu-ray discs, or 1ish triple layer Blu-ray disc. The problem here is that, the more layers required, the most expensive pressing those discs is going to be. It might be a few cents for those extra layers per disc for whatever publisher, but when you factor in the sheer number of discs being manufactured (ie: millions) it just adds up to way too much production cost for the amount of budget a large AAA game might have already spent in developing the game itself.
Now are there games that would totally fit on a cheaper dual layer disc, but the publisher can't be bothered to actually shell out the little extra cash for that? Absolutely, and those publishers are just being greedy shits (no fucking duh, they're a business, they're out to make money not be your friend). Is it some big issue in 2018 when most of the gaming market has access to high(ish) speed internet? Not really.
Nintendo will have this issue worse off than the PS4/xboner for future "large" games (assuming any devs can bother gimping those large games to run on the Switch, that is), purely because their cartridges are incredibly more expensive to produce with a smaller max capacity, so any large size game is basically going to guarantee a required download. There are already games that aren't fully on the cartridge, and I expect that practice to continue throughout the Switch's lifespan.
The worse is, really the only way to fix that issue and push more publishers into providing a whole game on disc is simply upping the base price of a game to cover those exponentially higher production costs. Would you rather spend $80 for a AAA title, just because games have gotten infinitely more complex and huge and require higher capacity, and therefore more expensive, discs, or keep spending the usual $60 and have to download a part of it for a few hours?
Some people would probably answer "sure, I like physical games enough to spend extra money!" But the average consumer doesn't give a rats ass, or at least enough to do anything meaningful, so nothing will change.
I personally prefer digital titles, simply because I don't care about cheap plastic cases and artwork I could just print myself. I have 0 actual risk of losing any of the titles I buy like I may with physical copies, and I don't have to dedicate some significant amount of physical space for all the games I might buy, so meh.