The Xbox retail version of Baldur’s Gate 3 will indeed have 4 discs, since we’re 500mb over the limit for 3. Only option would have been to cut some content out but that didn’t make sense...

It'd be cool if, ya know, digital releases came with transferable, irrevocable licenses, and the freedom to create your own physical backups for your games without needing to "check in".

But we won't get that. We'll never even get close to that.

So in lieu of that, we have to stick with the discs, because that's the last distribution method where there were proper consumer protections in place.

We're stuck with this dated format and it's low storage space because these businesses have utterly refused to provide us the same benefits in the digital space as we got from the discs, and the trade-off for the convenience is unacceptable.

"Cartridges" which are just SD cards in reality are a thing
I do not own Xbox ever, how does disc media work if you do not connect the console to always-on internet presumably for patches?
- IIRC, first time setup with the Xbox requires internet connection.
  
  When you buy a CD game, you still have to download part of it from the internet. The game will begin downloading and then can let you play when it reaches a certain percentage and continues downloading the rest of the game.
  
  I’m not sure about the Xbox, but other consoles have required certain updates for the console’s OS. I remember this being a thing with the PSP and PS3, in particular. Trying to stay on 3.55 for PS3 was a dream for many because it was hackable but some games required a higher OS version and the game couldn’t be played until the workaround was found to spoof an OS update.
BG3 is available DRM-free on PC. I'd say that's better than any sense of security offered by physical media.
But we won’t get that. We’ll never even get close to that.

Not for money, anyway.

Physical games should just be read only ssd or similar at this point. Maybe with a writable partition for updates and transferrable saves.

So a cartridge?
The economics don't work out - you have remember, optical discs are dirt cheap. Sony barged into the console market by guaranteeing any randos that passed certification could press as many copies as they wanted, with three days of lead time, for a dollar apiece. N64 cartridges cost ten bucks empty and you wouldn't get them for a month.

There is a reason Nintendo Power never had Game Boy demos glued to the front cover.

For Baldur's Gate 3, that third disc might be more expensive than the first two combined, because they have to spend some extra cents on a case with the flappy middle part.
Do you have any idea how much more expensive flash storage is compared to discs? There's a reason cartridge based gaming systems are limited to handheld nowadays. An 8GB switch cartridge costs about as much as a 50GB Bluray, from what I've read. And a 32GB card about 60% more. And the switch cartridges don't exactly use SSD quality NAND chips and controllers, which would be needed for the ever growing need of SSD speeds on current gen hardware.

So unless you're fine with paying double for your games, don't expect them to come on high quality cartridges any time soon, especially if we're talking about games over 100GB, which are getting more and more prominent.

You know, Baldur's Gate 1 was on 5 CD-ROM, 6 with the extension.

Of course it was mostly because it was a mess of mostly uncompressed graphics and audio, but still.

If I remember correctly the backgrounds were just fully drawn as huge bitmaps. Several of them for each area too, because they used separate bitmaps to represent collisions too.

I remember how big of a deal FF7 being on 3 discs was.
- On PC Lands of Lore 2 was on 4 discs, about at the same time (1997).
  
  It was a big game, but of course lots of video and fully voice acted dialogue mostly explained the need for all those.
  
  Most of the human/human-shaped characters were actors in FMW, often directly green-screened over the 3D environment. It was quite a surprise, I had never seen live action FMV used in a "real" game that's not some sort of point and click.

Given the history of the series, I find this to be pretty endearing. I have fond memories of playing the multi-disc Baldurs Gate 1 on PC as a child. It's kinda fun to see that today's gamers will have a similar experience with the same series nearly 30 years later.

As of Xbox One/PS4, all disc games are fully installed to the HDD/SSD, so you'll most likely have to sit through a lengthy install process. Not sure how fast the drive is, but it's probably 6x, meaning a theoretical 27 MB/s read speed, which in reality is probably averaging more like 20 MB/s. So the installation will likely take more than two hours.
It'll not be swapped during gameplay, but upon installation. RDR2 was similar.

I have never played that but I thought that it would be fairly small.

Doesn't Xbox use what's essentially 4k Blu-ray's for games? Those Blu-ray's have a pretty big capacity.

My PC install is 145GB, probably less on console but still quite large

surely they could have shaved-off 500 megabytes out of... what? 150 gigabytes... of game content and media just from better compression or optimization of those files.