Seagate has introduced the Exos M series, a range of enterprise-grade mechanical hard drives available in 30TB and 32TB capacities. The two models, the 30TB CMR ST30000NM004K and the 32TB SMR ST32000NM003K, each offer a minimum of 3TB per disk and use a standard 3.
The reason is transfer speeds. SATA is slow, M.2 is a direct PCIe link. And SSDs can saturate it, at least in bursts. Doubling the capacity of a 2.5" SSD is going to double its price as you need twice as many chips, there’s not really a market for 500 buck SATA SSDs, you’re looking for U.2 / U.3 ones. Yes, they’re quite a bit more expensive per TB but look at the difference in TBW to consumer SSDs.
If you’re a consumer and want a data grave, buy spinning platters. Or even a tape drive. You neither want, nor need, a high-capacity SSD.
Also you can always RAID them up.
For the context of bulk consumer storage (or even SOHO NAS) that’s irrelevant, though, because people are already happily using spinning mechanical 3.5" hard drives for this purpose, and they’re all already SATA. Therefore there’s no logical reason to worry about the physical size or slower write speeds of packing a bunch of flash chips into the same sized enclosure for those particular use cases.
There are reasons a big old SSD would be suitable for this. Silence, reliability, no spin up delay, resistance to outside mechanical forces, etc.
Sure it makes sense: Pretty much noone, but you, is going to buy them, and stocking shelves and warehouses with product costs money. All that unmoved stock would make them more expensive, making even more people not buy them. It’s inefficient.