Most of T-Series' subscribers come from people creating accounts in India and getting automatically subscribed to T-Series by YouTube's algorithms.

YouTube did this a while back with other demographics. For instance, CaptainSparklez often mentions this as one of the reasons why he became big; i.e. YouTube was autosubscribing folks to certain creators.

EDIT: If I recall correctly, when you create a new YouTube account, they give you a list of channel suggestions that you can check off to bootstrap you into suggestions based on your preferences, so this could be that, meaning people just "select all".

One Pewdiepie fan created a USB device that automatically unsubscribes from T-Series when plugged in: https://www.reddit.com/r/PewdiepieSubmissions/comments/a0ldp...

Here's one that auto-subscribes to Pewdiepie: https://www.reddit.com/r/PewdiepieSubmissions/comments/a0wcd...

Source code: https://github.com/Alone2/SubscribeToPewdsScript/blob/master...

Usually they are automatically checked off, and you have to manually uncheck every single one. Almost the same thing.

Someone also mentioned that PewDiePie was also gaining subscribers at the same time[1]. Either both of them were using bots or maybe Socialblade is not that accurate. I think something else is the reason behind it as others have pointed out.

1. https://twitter.com/sergevanred/status/1052381733172244480/

I doubt it, they've been around since 2006 and they're a very big label in India. It makes sense.