Do it, please. Very curious.
Very well.
2 discs
First of all, we need to look at how games are printed. Starting with the obvious, a production line is required to print games. To do that each production line is required to be calibrated in order to complete a print. Meaning they cannot switch data in and out like a USB. Each data needs it's own offsets. So at any given time, a production line can only print a single game. Production lines are also expensive as well, so it's not a case where there are dozens of them. I do not know whether SE has their own lines, or if they outsource printing. However, either way is is still limited. If they have their own lines, then it would most likely be just a few. Production lines run on schedules, meaning each line has a purpose to print something specific. You cannot simply add another print in without delaying this schedule, that is why delays with games have a much bigger ripple effect than people may think. It delays everything.
If they outsource printing, then there may be more production lines, but most likely they are printing many other things too, not just games. It's slightly more expensive as well.
To print more than one disc for a single game would mean almost double the increase in costs. It would require multiple production lines offset with unique data. Using another line would also mean it cannot print another different game. And as I said, production runs on schedule. Pushing two lines for one game would mean pushing another out. This creates a big imbalance in cost to performance. By using a line that can be used for something else, you are essentially losing productivity. Which as a business, is a bad thing.
Another thing is how much you can actually utilize the second disc to make it actually worth it. If the second disc only takes 10GB that becomes a waste. And to fill it up more, say 30GB, you would need to develop more content, which means taking a lot more time in development. If you manage to fill up two discs, you are developing two games by industry standards, for the price of one game.
Also, unlike the PS1 era where it required the actual disc to be in the console to work. The core data files were duplicated onto every disc, likes character models etc. This wasn't as much of a problem back then as when you switched through the disks, as this allowed you to access almost everything on disc one on disc four. However, now, that's a different story. Data files have gotten much larger, so you would have to use a large portion of the disc to even just duplicate all the required codes and data. But this isn't a problem as we install our games into the console. However, another problem surfaces. If in example, a game is 90GB split into 2 discs, that will eat up a lot of HDD space. And most people don't upgrade their storage and if the industry use multi-disc games as an actual standard, we'll be running out of space real fast. This will be an issue for those wishing to use SSD's, which are much more limited in storage compared to HDD's. This will affect downloads as there are already plenty of people who complain about seeing days to download 7GB's. Imagine trying to download 90GB.
You can kinda solve the install issue by keeping the game on disc and not installing it. But this would increase loading times and this creates another issue.
You cannot simply split a 90GB game into 45/45 into two discs. If you want to access the areas you accessed in the first disc in the second disc, you would need to duplicate all of the data assets. So if data assets are 40GB of a 90GB game, that needs to be duplicated into 2 discs and the remaining data needs to split accordingly.
Doing the math (theoretical)
90GB Game 40GB asset data + 50GB content data/other
Disc One 40GB + 25GB = 65GB
Disc Two 40GB + 25GB = 65GB
As you have noticed, both exceeds the data limit. So you require a third disc, in which you need to duplicate the data again. In which might require a fourth. It's not exactly simple math.
TL;DR Point being, the industry is simply not set up properly to take this route.