Not stupid at all.
It is a collection of drivers that match PC hardware such as CP5611, CP1613, or other hardware.
And it is also a part of Siemens "PC Station" concept. This is a virtual backplane where various components can be inserted, such as drivers for the aforementioned hardware, the WinAC soft-PLC, the OPC Server, and bridges to WinCC and WinCC Flexible.
When you purchase a Simatic Net license, you purchase the right to use it with a specific hardware and often in a specific mode. For example Simatic Softnet Profibus S7 works with CP5611 and CP5621 cards and using the S7 protocol with Profibus.
With each license you also get the right to use Simatic Net as OPC Server.