How many people complains about memory corruption? This is a ridiculously rare issue, which impact is minimal, if not null, for so many people. There's an actual cost to provide ECC memory though, there's actually more hardware necessary to cover it. Obviously if more would need it, it may lower the cost because of the scale, but it will still be more. For some it's important, and for sure they will pay for it, so let them pay for it...
It's not like it wasn't available, Linus just forgot to put a reminder to buy some once available (backordering them would have been even more prudent).
Ridiculously rare? That's why CDs, DVDs, blurays, caches, SSDs, spinning rust, etc all have ECC, right? Even ancient file transfer protocols like xmodem and zmodem has error correction.
Bitflips aren't uncommon, it's just compression makes them much more noticeable. Without compression users might just see an occasional application crash, and just relaunch the proces.s Seems common for people collecting photos, music, etc for years go back and find some corrupted. It's hard to say exactly what happened, but with compression a bit flip it turned into a seriously corrupted file.
Keep in mind that, radiation caused bit flips are rare, some failure in the chip, pin, dimm, dimm connector, motherboard, CPU pin, CPU are much more common. It's MUCH nicer to see "error on dim X, row Y, column Z" then a randomly crashing machine. Even Linus sounds like he spent hours tracking it down, and thought he was hitting a kernel bug.
Isn't it worth 1/9th more memory chips to make the system robust in the face of wide variety of errors that can corrupt memory, which can lead to corrupted storage?
It's not like it wasn't available, Linus just forgot to put a reminder to buy some once available (backordering them would have been even more prudent).