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Modern devices have tiny features which are extremely fragile to any sort of interference, which are much more abundant than cosmic rays.

See the row-hammer attack where you can flip an unrelated bit just by read/writes to adjacent bits from software!!!

[Beltalowda]

This is also why memtest has all these testing patterns, and one reason why you typically want to leave it running overnight (or as long as feasible) instead of "yup, we read and wrote all bits and it's all fine!"

Row hammer is one of those things that took advantage of something everyone already kind of knew, just never thought about as a security problem.