keymailer does not set any thresholds or criteria other than for gaining accreditation.
Game Publishers decide who to give keys to.
They normally filter our unaccredited channels, filter by things like country, genre, popularity, then offer keys.
But some developers, especially indie devs, will offer keys to unaccredited channels, and are pleased to have any YouTubers or Twitch Streamers offering to make coverage about their game.
So keep trying!