Right, but a huge part of the consumer SSD space has moved to m.2, where there isn't a lot of space to just pack in another couple dies. While conceivably you might be able to make a 8TB drive in m.2 its going to be easier in 2.5", and people with the money to buy that large of a SSD probably don't want it on SATA. Which is why, as you point out they exist, here is a 8TB u.2
https://www.newegg.com/Product/Product.aspx?Item=1E4-006U-00...
for only $2600.