What are two possible reasons an ESXi host cannot be removed from a vSphere Distributed Switch (VDS)?

An ESXi host cannot be removed from a vSphere Distributed Switch (VDS) primarily because it has virtual machine network adapters that are currently connected to the switch. When virtual machines are linked to the VDS, they rely on that network infrastructure for communication. Therefore, the ESXi host must first have all of its attached virtual machine network adapters disconnected or migrated to another network before the host can be removed from the VDS. This ensures that there is no disruption to the network connectivity of the virtual machines that were operating on that host and connected to the distributed switch.

The presence of the virtual machine network adapters ensures that removing the host could lead to network issues, as the VDS is responsible for handling the network packets for those VMs. Thus, it's a requirement to either disconnect or migrate these adapters to maintain network stability and integrity within the virtual environment.