Mezzanine modules are an important gaming platform element to many board form factors. They grew out of a necessity to gain more board real estate or to incorporate modular flexibility to the original form factor. In the early days, few, if any, standards for mezzanines existed. However, over time, standards emerged to make it easier to incorporate mezzanines into designs.
Ecosystems for various mezzanine form gaming platform at various levels, making some more popular than others. Companies still continue to develop proprietary mezzanines to meet specific requirements, and this is expected to continue as long as board-level components exist.