The practice started with Indira Gandhi and is religious followed till now. For example, whenever national party president has to be elected (in practice enacted), Congressmen even dare not to think beyond Nehru-Indira family and their scions. For a short while, Congress experimented with leaders from non-Nehru-Indira family but it didn't work. And ultimately, Congressmen were left with no option but to knock the door of, "videshi bahu of desi putr", Sonia Gandhi. She led the part from front from 1998 to Dec 2017. And as is the GOP practice, She was succeeded by her son Rahul Gandhi. For Congressmen Nehru-Gandhi family scions are the best bet.
Another typical Congress is that whenever a non-Nehru-Indira family leader emerges, he is either cut to the size or dies while blooming. From Sardar Patel, Lal Bahadur Shatri, Kamraj, Devraj Urs (both from South ) To P. V. Narasimha Rao, Rajesh Pilot, Madhavrao Scindia.
P. V. Narasimha Rao's ascendancy to the prime ministership was politically and economically most significant. It saw a paradigm shift from the Nehruvian model of industrialising, mixed economy to a market driven economy. He was a versatile personality with interests in a variety of subjects and spoke 17 languages. Dr Manmohan Singh, longest non-Nehru-Indira family PM was his choice and inducted as Finance Minister. Roa was also referred to as Chanakya for his ability to steer tough economic and political legislation through the parliament at a time when he headed a minority government. Unfortunately, he died a unsung death, Congressmen too obsessed with Nehru-Gandhi family even forget to pay tributes to this man who steered a almost bankrupt nation from economic collapse.
Rajesh Pilot was a mass leader from Rajasthan but died mysteriously in an road accident. His son Sachin Pilot succeeded him and has emerged as tall Rajasthan leader. Madhavrao Scindia, nine-term member of the Lok Sabha, Madhavrao Scindia never lost an election.A nine-term member of the Lok Sabha, Madhavrao Scindia never lost an election since 1971. During Janata Party wave of 1977 when Congress was abysmally routed in Hindi heartland, Scindia won as an independent from Guna seat in MP. He was the President of the Board of Control for Cricket in India from 1990 to 1993. He died in a plane crash, His son Jyotiraditya Madhavrao Scindia was anointed his successor.
Both Sachin Pilot and Jyotiraditya Madhavrao Scindia were Congress chief ministerial candidate in MP and Rajasthan respectively but I am sure will be denied the post by party high command led by a young national chief, Rahul Gandhi. Congress top leadership engrossed in Indira Gandhi can't see state leaders emerging more popular than national leadership. Sachin and Jyotiraditya will be no exception.
To exert its supreme authority and cut emerging regional leaders to size, Congress top leadership has devised a way: Send central observers with a brief to pass a one line resolution to authorise Party national president. who happens to be Nehru-Indira scion, to choose state legislative party leader. This drama is being enacted by Congress Since Indira era. this practice is religiously followed, Congress under Rahul Gandhi is no exception.