Answered by Jacob Laukaitis, marketer
For the Slums of Mumbai video, I got a little bit of press on websites like this: https://www.boredpanda.com/living-in-mumbai-slums-jacob-laukaitis/. YouTube's algorithm also noticed that my subscribers as well as new people were engaging very well with the video (they would watch it over 42% on average, the like and comment ratio was also really good).
It started featuring the video to other people who were interested in the topic. Initially to just a few thousand people, then to some more, and now that the algorithm knows that a lot of people enjoy this video, it gets featured to a lot of people searching for the slums of Mumbai and related things. Even if you search for "Slums of Mumbai" on YouTube, that video should come up somewhere near the top.
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