Why can't I deliver my Release using more than one digital distribution company?

The more the better? Not always.

Just like in the physical world, there shouldn't be more than one digital music distributor bringing the same Release to the same store. Otherwise, when the Release makes some sales, how would the retail store know which distributor to pay?

However we can not prevent you from doing anything you want with your music.

But it is in your interest to be made aware that if you sign two digital distribution deals with two companies that will both be sending the same Release to iTunes, Spotify, Amazon, etc - this can have some serious consequences since the retailer will remove the Releases completely until you decide which distributor has the exclusive right to be selling that Release through them...