Why on a PC with Windows 8+Debian+"grub2-pc" when upgrading from windows 8 to windows 10, the Windows bootloader did not overwrite Grub? Is my guess correct?

Question

MBR

Why on a PC, on the hdd (mbr markup) of which win8 + debian + "grub2-pc" were installed, when updating win8 to win10 (namely, updating and not installing over), the Windows bootloader did not overwrite the rough entry (which is in the mbr of the disk) with an entry referring to your screw loader?
My guess:because win8, when I upgraded to win10, I thought that mbr already registered (even when installing win8) its (windows) bootloader (and its windows drivers for understanding NTFS, which did not change in win10 either), and therefore Windows did not do " the thing that had already been done when installing win8", did not begin to register the bootloader in mbr, which (as she thought) was already written there (she did not know that grub was now written in mbr). Thus, Windows limited itself to updating the bootloader itself, which is located on the hidden “system reserved” partition, but grub (as you know) is installed on a completely different partition. That's why the rough remained unscathed and successfully starts when you turn on the PC. So?

Answer 1

From the point of view of Windows, her bootloader is where it should be, she simply does not know how to recognize *NIX bootloaders.