UEFI firmware provides the first stage bootstrap, which searches for the second stage bootstrap in a folder /boot/efi. The UEFI specification requires the file system holding this second stage to be a FAT based file system; however, Windows is normally installed in an NTFS filesystem, which a UEFI firmware may not support, although some computers may have firmware that can access NTFS file systems.
To ensure that Windows can boot on any 64-bit UEFI computer, Microsoft introduced a separate EFI partition that has the required file system type, but is inaccessible to Windows. The second stage bootstrap in Microsoft's EFI partition can boot Windows from its NTFS partition.
There is another reason why Microsoft use a separate EFI partition. If C: is BitLocker encrypted then there has to be a bootstrap that is not encrypted but can unlock and access the BitLocker encrypted C: file system.
I hope this helps.