The modern OT threat landscape is growing due to the significant rise of interconnected network devices. OT is particularly vulnerable given the need for high availability and integrity, at the expense of confidentiality (which is at odds with the priorities in an IT environment). Following the Purdue model helps mitigate the risk of compromise by not allowing different types of devices to operate on the same subnet (eg: manufacturing devices and databases). Consequently, it is referenced in key compliance standards such as IEC62443 and OG86 as a practice to be implemented.
OG86 - The Health and Safety Executive's Guidance for Industrial Network Security
OG86 is Operational Guidance issued by the Health & Safety Executive (the UK government agency tasked with regulating and enforcing health and safety in the workplace) to mitigate the risk of cyber-attacks that could result in health and safety incidents, major accidents and/or the loss of essential services.