I do think they reach millions, how many indies do you know of. And we even has had confirmation that even corpo vtubers and voice actors/non-vtubers apply to hololive.
Also hololive round 1 is actually open knowledge. You submit a video, kinda like a mini youtube. If the video is interesting then they proceed with interview. If the video is boring as fuck they click away and move on. It isnt surprising she only got interviewed once. As the previous attempt she even acknowledge they were cringe.
The 7th attempt being passed may due to they already having found nerissa and liz who are a million times better singers and they arent interested at MVs and value other qualities
Dont understand your 2nd point about the US. Hololive dont narrow down their criteria because they are looking for variety. Not programmers who will do a very specific coding work or lawyers who practices a specific field. It's in holo best interest to have things being vague so that they have more type of people/personality to pick from