Because the LBP-1120 is a host-based printer? Correction: It is actually a winprinter (Windows Printer) that relies on the host PC’s CPU for rendering. This is why it is tricky.
: This is the most reliable method for older hardware. Canon Laser Shot Lbp-1120 Driver Windows 10 64 Bit
This is the most reliable method. By running a "guest" 32-bit operating system inside your Windows 10 environment, you can install the original 32-bit drivers and share the printer with your main machine. Because the LBP-1120 is a host-based printer
This method bypasses Windows driver issues entirely because the Pi handles the rendering. Canon Laser Shot Lbp-1120 Driver Windows 10 64 Bit