Because skill differ too much. It is easy to create union in manufacturing because everyone is doing roughly the same thing. There is very small variation in s

Because skill differ too much. It is easy to create union in manufacturing because everyone is doing roughly the same thing. There is very small variation in skill in majority of workers. It is similar in Law or Medicine where you have standards and exams for these professions. In programming you can have home growth hacker that produce just another PHP website every week or Machine Learning expert working with distributed systems, publishing papers or contributing to projects like TensorFlow. It will be extremely difficult to persuade both of them to take the same stance on earning or job protection. One is remote developer making 20k per year and second is Google developer making 300k. Union represent group of people, but it is important to remember that you transfer part of decision power to Union in exchange for better bargaining power. Google developers do not need Union because they have high personal value, they can easily change jobs and still make a lot of money. PHP/Web developers that are commodity would benefit from Union but disparity on skill and background will make it impossible to happen. In general Union are for people that are insecure about theirs jobs. In many cases Unions are actually harmful. Teachers Union in my home country makes impossible to fire bad teachers. It is major issue where instead of teaching results, tenure is more important. Train workers unions are equally bad, low skilled workers demand high compensation.