Modbus is a very easy to learn protocol and also a widely accepted communication standard. Additionally, it is an open source protocol which makes thousands of API’s to be available in the internet for every single programming language. Modbus is very easy to use and to integrate in any existing network.
On the other hand, Modbus over TCP/IP is very reliable, meaning it does not need to be set in network. Any master will know when a slave has been disconnected.