I think broadly speaking governments do a lot to set the tone of what's acceptable in the pandemic, by what they say, and what they do. A big government rally is powerful legitimation for being selfish.
I don't think there is enough evidence (yet?) to call any one factor a "key contributor". We simply don't know. People in India were increasingly mobile as their pandemic conditions improved into a low steady state (https://ourworldindata.org/grapher/changes-visitors-covid?co...). I am guessing that some combination of the things you listed, plus general increase in mobility, plus some new variant of the virus that spreads more easily, is what led to this situation. India went from normal conditions to hitting the previous peaks within a month, and that feels like something more than just a few isolated events.
> This situation is really a reflection of the selfishness of the people.
That might be fair to say in a developed nation that is wealthier. But in many other nations, people simply need to work or go to places where they are around other people. They don't have the infrastructure, wealth, and luxury of remote work or delivery services to just avoid society altogether or reduce society-wide mobility. They also don't have the same amount of home entertainment choices like streaming services or expensive video game consoles or whatever else. I imagine shutting down cities is a much more significant challenge in places that are denser than, for example, American cities, but without the same economies, standards of living, disposable income, and so on.
1. Election rallies
2. Kumbh Mela
3. Farmer Protests (Yes, they are still going on)
4. The government's incompetence.
And all of these are completely valid reasons. But does anyone living in the country really believe that these are the only reasons? There are still people who believe that Covid is a hoax. People who had not worn a mask for the last 6 months now wear paper thin masks in large crowds and expect to not get Covid.
My neighbor contracted Covid recently, but they have not told anyone about it. All of their household help is still coming. Some of the family members still go out to meet others.
This situation is really a reflection of the selfishness of the people. I have seen medium-sized business that cut salaries if employees take leaves due to covid. So these employees hide their symptoms and report to work. If you are doing any of these things, please self-reflect.