Infrastructure Software includes those capabilities allowing access to downstream devices such as endpoints. There is the virtualization aspect of cloud, the application/identity management for administrators (think just enough access when they need it vice all the time), and security management. Since most, if not all, companies are some forms of hybrid living both on premises and in the cloud, there is a strong chance of legacy devices.
Everything is now interconnected in some way and companies have to be aware of both smart and “not so smart” devices sitting in their area of responsibility. We have the internet of things (IoT) where connected devices could have their own unique identities and then we have Industrial IoT (IIoT) which is a network of smart devices having their own computing power. You cannot secure what you cannot see so we look for companies helping with telemetry, observability, and reporting what an organization is actively using and has under their purview, not just what they think they have.