The T-Series and PewDiePie War
The basic premise is that the most subscribed Youtuber PewDiePie is about to get passed by the MCN (Multi-Channel-Network) T-Series. Not a big deal, right? Well, the thing is that first of all PewDiePie has been at the top regardless of whether you want it or not. Second of all, Youtube has changed a lot. If you take back a step and look at Youtube the way it is currently evolving may be shocking. The interest in TV has been decreasing and the interest in Youtube skyrockets. This means that more and more companies will or do move to Youtube instead (for obvious reasons). That means that there are a lot of changes, cooperate deals, more companies on Youtube, etc.. One of them being T-Series an Indian MCN. So two big things are happening here now.
Conquering India
Since India is getting Internet access now, big companies, such as Google try to capture all the potential customers and catering them Youtube seems to be extremely successful, hence the growth of the T-series channel
Multi-Channel-Networks
Due to a lot of some-shady some not so shady occurrences, MCN or multi-channel-networks don't have the best reputation. Especially since the whole Defy Media story. However, the more channels they combine the more content, with higher quality at a higher frequency with a vaster grip they can produce in less time. This allows them to grow much faster, which in turn brings fame to smaller channels. This allows T-series to grow really fast.
I Don't Like PewDiePie, Why Should I Care?
It's not like the internet had an option. Aside from his current content catering to a wide audience (PewNews or Book Review covering more serious topics and Meme Review catering to the internet culture basically) he is the most subscribed individual on Youtube. If there's someone to keep above a cooperate channel it must be someone who already has the most subscribed and has not been passed yet. This is how the current situation has ended up.
Even if you do not like PewDiePie, subscribing to him is a metaphor for showing that you want the individual to be above the cooperation. This is what this symbolizes.
And as Matthew Patrick from GameTheory and FilmTheory said in one of his streams.. we can only do this now. Once T-series has passed it's over and there is no back.1
Additionally, if you don't like PewDiePie for what he has done and because the media associates him with Nazi... he knows his mistake and has changed. He has done his part now it's time for you to do yours. It's not like he meant it. (Also Germans make fun of Hitler too...)
1 https://www.youtube.com/watch?v=prhVME-0vLI