In the Destiny community, this process is called the "Content Vault" - deleted materials, including the "Red War" campaign, the "Curse of Osiris" and "Warmind" expansions, several raids, and the Forsaken campaign, were seemingly sent to a "safe."
Max Nichols, a former Destiny developer, described the "content vaulting" process and his role in it on his website. Nichols worked at Bungie for over 9 years, creating new missions and modes, updating old content, and participating in the Content Vault.
According to Nichols, "Beyond Light" brought a major engine update that was incompatible with all existing materials. Content had to be re-transferred, counting labor costs and the number of new employees. Nichols personally oversaw the hiring of 20 junior technical designers.