[10000truths]

A "regular file" might reside in multiple locations on disk for redundancy, or might have a checksum that needs to be maintained alongside it for integrity. Or, as you say, its contents might not reside in contiguous sectors - or you might be writing to a hole in a sparse file. There's a lot of "magic" that could go on behind the scenes when operating on "regular files", depending on what filesystem you're using with what options. Directly operating on the block device makes it easier to reason about the performance guarantees, since your reads and writes map more cleanly to the underlying SCSI/ATA/NVME commands issued.