Because a laptop often uses a hybrid solution or a combination of a Intel video solution for most 2d display features.
And a mini Pci-e based mobile 3D graphics card solution such as the 920m Nvidia Gpu.
You cannot download and use the drivers in some cases provided from the Nvidia latest download driver section.
Instead you have to go to the bran maker of the laptop, with the model number of that laptop in question.
And download and install the drivers provided on there support site for drivers for your model of laptop to get the 920M chip set to be detected and the driver to install Sam.