What you're talking about already sort of exists, albeit media hadn't reached "cheap" yet, because the manufacturing scale wasn't there. People weren't interested enough in it. Archival Disc was a standard that Sony and Panasonic produced, https://en.wikipedia.org/wiki/Archival_Disc. Before the standard was retired you could by gen3 ones with 5.5TB of capacity, https://pro.sony/ue_US/products/optical-disc-archive-cartrid...
LTO tape was already at 15TB by the time their 300GB Discs came out, and reached 45TB capacity 3 years ago. Tape is still leaps and bounds ahead of anything achievable in optical media and isn't write-once. (https://en.wikipedia.org/wiki/Linear_Tape-Open)
Part of the problem is you can't just store and forget, you have to carry out fixity checks on a regular basis (https://blogs.loc.gov/thesignal/2014/02/check-yourself-how-a...). Same thing as with your backups, backups that don't have restores tested aren't really backups, they're just bitrot. You want to know that when you go to get something archived, it's actually there. That means you're having to load and validate every bit of media on a very regular basis, because you have to catch degradation before it's an issue. That's probably fine when you're talking a handful of discs, but it doesn't scale that well at all.
The amount of space that it takes for the drives to read the optical disc, the machinery to handle the physical automation of shuffling discs around etc. combined with the costs of it, just make no sense compared to the pre-existing solutions in the space. You don't get the effective data density (GB/sq meter) you'd need to make it make sense, nor do the drives come at any kind of a price point that could possibly overcome those costs.
To top it all off, the storage environment conditions of optical media isn't really any different from Tape, except maybe slightly less sensitive to magnetic interference.