In simple terms, a scatter file is a roadmap for the SP Flash Tool (the standard flashing tool for MediaTek chips). It tells the computer:
Never use an MT6572 or MT6735 scatter file on an MT6582 device. This will likely hard-brick your phone.
This example provides a simplified view, but actual scatter files contain more detailed information specific to the device's memory layout.
They have different memory mapping and DRAM configurations. The flashing tool will fail.