Don't worry too much about things like this if your credentials are fine. When you have 10 similar applicants for 1 spot the decision is basically random. Especially when its only a 2-day event, management/HR aren't going to spend hundreds of hours trawling through applications to reach a decision. Unfortunately random rejections are a fact of life when applying for things like this.
Its the same when applying for VS and TCs, you can easily make 12 applications and get accepted by the best firm on there but rejected by the rest.