Yeah, but their usage is vaning fast in all their usage scenarios, hence why it's getting more expensive. Also, optical discs ain't interchangeable in production, you need specific presses for specific discs, a Blu-Ray press can't make CDs or DVDs, at least not out of the blue. Discs very much gain from mass production, because the machines to press the discs ain't cheap, and slower production raises costs very fast for them. The problem is that there are so many producers slowing each other down as the demand vanes.
For AAA games, 4-8GB discs are useless, I agree. But for Indies or Retro game collections, they do suffice most of the time. And yeah, we are moving more and more away from discs. Try finding a laptop with an optical drive these days, it's getting more and more difficult. Steaming and digital formats are taking over, and optical discs are more and more becoming a niche product. I'll have to dig to find the source, but afair the sales of Blu-ray discs is close to the one of DVDs in 2000 when VHS tapes where still ruling the market. The economy of scale which is making the optical discs so cheap less and less applies to them.
It won't affect the PS4/XBO anymore, though. But it could affect their successors. Getting more than 100GB on an optical disc is proving to become impractical (UV lasers get stopped by the slightest dust particles, hence why a blue laser is the practical limit for end-users), but with increasingly bigger textures and game worlds, that won't be enough for long anymore.
By contrast, cartridges don't face such a brick wall just yet. Expect them to catch up more and more over the next couple years. I think by end of this year, it won't make much of a price difference between a 25GB Blu-Ray disc and a 16GB cartridge, with the 32GB following close behind.
In fact, I wouldn't be surprised if someone would come up with a new standard next to SD cards (since Secure Digital isn't anywhere near secure) with a similar size, but much more safety. If they could get the Film Industry on board (which will be looking for a medium for 8K movies in the future for sure), then this could quickly replace the optical discs in general usage.
I'm really not sure what your point is given the platform primarily suffering from an expensive storage medium is Switch. Sometimes Switch ports are more expensive, developers avoid using large carts and publishers are clearly avoiding physical releases. I agree we're moving away from optical discs, but they're still cheaper to produce than Switch carts. In the past platforms like Dreamcast, Gamecube and PSP used unique discs which shows mass production may not be that crucial. I believe optical discs are just inherently cheaper to produce when compared to memory carts that hold a significant amount of storage.
I anticipate the 100GB discs will be used in the 9th gen consoles and will be plenty of storage space for most games. It would help if more games split online and offline content, that way a disc just needs to hold the offline stuff. Maybe by the 10th gen there will be dirt cheap carts that hold a massive amount of storage. Until then though, discs are still the cheap route.
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