I’m no expert, but my understanding is that bits can “flip” and introduce errors due to things as unpredictable as background radiation etc, even on files the system has had no interaction with, which is why it’s kind of desirable to implement this kind of integrity check at the file system level. A higher level check may be completely unaware of this kind of passive background error.

Also, if I pull the drive and move it to another machine, again it’s kind of nice if the data integrity features are tied to the drive format rather than higher level software. I don’t think it’s too unreasonable to expect the file system to make sensible guarantees that the sequence of bytes I record today will remain the same until I next interact with them.

I’m not sure how appropriate comparisons with IP error correction is either; it’s a markedly different class of problem really (you are not dealing with long term storage issues at all).