Ata Cable Why Is There A Concept Of 'maximum Cable Length' When It Comes To ATA Cables?

Why is there a concept of 'maximum cable length' when it comes to ATA cables? - ata cable

For example:
"Parallel ATA standards allow cable lengths of up to only 18 inches.
Why is there a limit?
Will 20-inch PATA cable, for example, is working as expected?