Why various firms in foreign countries have closed some of their specialist departments and handed over to the companies situated in other countries?

Due to outsourcing

The answer is option 3 i.e. "Outsourcing". Outsourcing of work is becoming a common practice. It means that a big firm finds it profitable to close down some of its specialist departments (for example, legal or computer programming or customer service sections) and hand over a large number of small piecemeal jobs to very small enterprises or specialist individuals, sometimes situated even in other countries.