It says the credits needed is "based on game popularity, difficulty in training and history of updates from the game developer." So for a game like, say, Gigantic Army or Yaiba Ninja Gaiden Z that hasn't come out yet (at least no for steam for the former) how is the popularity, difficulty, and history determined (3500 credits for Gigantic Army! )?
It's written in the description. It's based on experience. If you take a look on the steam page you clearly see that it's a 2D retro based game which I personally never heard of. The popularity will be less. The other game from the same developers looks like the same game (at least same HUD) although it should be a different game which is a bad sign in my eyes.
My expected download count of a trainer is <50. I'm not defining the amount of credits but I'm sure PWiz feels the same and that's why 3500 credits are necessary.
Like I said many things have an impact on the decision about the credits. I wouldn't agree on your statement but what I can say for sure is that old games and/or games that are less played need more credits than popular games. But even popular games may need a lot credits for example the wargame serie that is known to patch thousand of times per week.
Last thing is, which Pwiz said couple of times, the request system is still in development.