High level teams train players, but they also spend a lot on players from the TL. It seems to me that it's the teams that can't compete with high spenders that need to rely more on their Trainers if they want to have any players making more than $30k, and those teams can't afford the best trainers. Granted, the top trainers tend to have higher salaries than most of the players on a given roster (but let's not put that issue into this thread!). My little interjection here is to point out that it's those D.III teams that probably have the biggest need for the best trainers, but who also have a difficult time bidding on them.
But maybe a Level 4 Trainer is good enough... without seeing the code, we can only conjecture, and we're never going to see the code.
Don't ask what sort of Chunks they are, you probably don't want to know. Blowing Chunks since Season 4!