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).