2 reasons:

1. The creator is extremely cool about remixes and fanuse. In many ways touhou is the OG modern internet fandom in a way that previous ones weren't. Your bad apple video will not be taken down even though it has the same audio as all the others.

2. The shadow puppet format is recognizable at seemingly any resolution. I have seen examples in a 3x3 grid even. On top of that, it only has two colors (black/white, 1/0) so its dead simple to convert the video frames into any other format you can imagine with only a 'hello world' understanding of what you're doing.