Till advent of Janta Party and Morarji Desai there was virtual single party rule. Even after Janta Party's elevation there was bipolar polity.
So when and how regional parties started becoming relevant. I think single most reason was total lack of intra-party democracy in Congress and autocratic streak of Indira Gandhi created all these regional satraps.
She could never tolerate any popular leader inside her own party. Some of them died (allegedly killed like Lalit Narayan Mishra of Bihar) in dubious circumstances when they were about overshadow Indira Gandhi. So when these congressmen figured whatever they do there is a ceiling beyond which they can’t aspire to go they broke off from the parent party. These satraps gave voice to the aspirations of local people. Every reason wants their leader to be elevated to the top post if he she shows competence but that was not possible under Nehru family thumb.
People started voting for regional parties because they saw their leader being treated with utmost disrespect with so called high-command raja-rani of Nehru family.
So if today you are anguished over ever-increasing fortunes of regional parties then blame congress and autocratic congressi culture bereft of any intra-party democracy.
Manmohan Singh exclaimed these regional parties are weakening centre. Well that actually was the idea in first place when Gandhiji asked for gram-swaraj it was to be total decentralization of polity. Instead what we got is more centralization than what we had during British. So Manmohan can cry in pain over his helplessness in catapulting his mentor to the PM post single-handedly but unless Manmohan keeps his family adulation streak intact regional parties are here to stay. Not everyone can have fawning worshipping streak towards a family people do have self-respect. If that mean voting for likes of Mayavati or Mulayam or even Laloo so be it.
So my message to congressi change your ways bring some semblance of intra-party democracy start respecting leaders other than Nehru family naturally polity will turn bipolar. Due to your sin even BJP has to suffer due to regional satrap's influence.
Then there is this unconstitutional streak of congress which drives them to take steps like emergency or indulges in flagrant buying of MPs. First time under Narsimha Rao rule of JMM MPs now under Manmohan Singh in congruence with characters like Amar Singh.
By contrast we have BJP who allowed a congress MP who was also Orissa CM to vote which was unconstitutional to start with. Had they wanted speaker could have easily barred him and that would have been constitutional step? Yet NDA left it to the morality of that MP and we all know how NDA govt lost by a single vote. IF NDA had wanted then throwing few crores would not have been an issue but then there is constitutional morality involved. IF Congress wants people to come back to their fold then they must apologize and shun their ways in future. But we don’t see this happening by hook or crook even likes of Manmohan Singh clings on to power.
Regional parties can't be wished away untill these unconstitutional practices continue.
Tailpiece: Manmohan Singh chimed he didn’t know about Tytler’s clean-chit by CBI. Now question needs to be asked. CBI falls under PM office so either he is not the real PM and hence he didn’t know or he is lying. Moreover doesn’t he read paper or watch TV. How can anyone not know that Tytler was given clean-chit by CBI? How can you lie with straight face? We tolerated your lie when Bofors kickback was released to Quttrochi a close relative of Sonia. But how long can we keep getting fed lie.
You are absolutely right in saying that lack of intra democracy in congress led to regional party. But I think there are many other reason like you mentioned too much centralization. But putting the whole blame on congress would be little unfair.
In my opinion it's our tollerance of feudal culture that is the root cause. Look at regional party came out of reaction to family raj over party. Take for example siv sena, TDP, JD(S), DMK, RJD, BJD, praja rajayam etc. All are like family enterprise. Why we as voter elect the MP or MLA just because he or she happens to be kin of ex-MP or so. Why is so that we elect people as MP who are considered loyalist to Gandhi family. Leave poltics aside, every aspect of our enterprise is filled with such examples be it big or small industrial houses or bollybood or any other aspect of life. We tend to pass on goodwill and brand value of self to other family members. I don't see any thing wrong in this but what disturb me more is surrendering our choices to family and elect/select some from the family or nominated loyalist without evaluating on merit. What we are seeing is just manifestion of our choices in life or to some extent similar to our caste system which we have choosen to continue with. If we want change in this then as the famous saying goes "we have to change our selves first". It. Has to start with me. May be external intervention would be required to get such changes quickly. I mean we can change constitution and require that all recognized party to have secret voting with at least three contenders. Also these election will be conducted by national or state election commisoner as appropriate.