Vulnerability management and patch management are not products. They are processes, and the products are tools used to enable the process. You cannot buy a hammer, nails and wood and expect them to just become a house, but you can go through the process of building the house or hire someone to do it for you as a service.
Vulnerability management and patch management products are often lumped together and assumed to be part of the same product. While they have a compatible relationship, they are not the same. Vulnerability and patch management products are distinct products with different purposes and goals that are used to support these processes.