From a supply perspective, 256GB seems ridiculous because you can get way more capacity for not very much money, and because 256GB is now nowhere close to enough flash chips operating in parallel to reach what is now considered high performance.

But from a demand perspective, there are a lot of PC users for whom 256GB is plenty of capacity and performance. Most computers sold aren't gaming PCs or professional workstations; mainstream consumer storage requirements (aside from gaming) have been nearly stagnant for years due to the popularity of cloud computing and streaming video.