Why are we not allowed to play as locked DLC heroes in custom match? You allow us to play with them in training mode to see if they fit our playstyle why not in custom match as well?

By just allowing the player blase to have access to these heroes and play with them on a much larger scale would help us decide if we want to buy that specific hero or not. Being in an actual match with dozens of different scenarios against multiple opponents is a huge deciding factor in what we want to buy.
Im just curious as to why this process of the deciding factor is blocked to us.