Take for instance, the Vinaya rule which prohibits a monk from travelling in a vehicle when not suffering from a sickness. According to this rule monks have to travel on foot when not physically ill. But today not satisfied with ordinary cars the Mahanayakas who should set the example are going in for Benz cars. Then there is the rule which forbids monks to handle money. This is not practicable in modern capitalistic society with a market economy.
Monks have to travel by private or public transport and pay the fare.
They have to pay for their medicines, the use of electricity and water etc. They have to teach in pirivenas, schools, or universities. How can they refrain from accepting their salaries. Take the case of a missionary monk who goes to a city in the West. This rule is impracticable in modern society.