The main reason we don't do anything like this is due to the sheer volume of applications that we receive. We receive hundreds of applications every week, we review them over the course of 2 weeks, and then make our final decision for that application based on when it was received as well as the quality of the content, viewer count, and if we think the channel would be a good fit for the programme. There are a lot on internal requirements based on how our partner team look for aspiring partners, however these are internal and cannot be discussed in detail.
Replying to each application manually would take a large portion of time out of our team's day, when they have other important duties to attend to such as infrastructure and helping to run other important areas of the network. While we do understand that receiving feedback is important it's just not something that we are able to do at the moment.
On an additional note senior moderators will sometimes end up providing a small amount of feedback if your helper application has been denied.