The Eternal Collection includes the Reaper of Souls expansion and the Rise of the Necromancer pack. Because the XCI is a full dump of a cartridge that already contains all DLC data (unlike an NSP which might require separate ticket files), it is a "complete-in-one" file.
: Official game releases contribute to the financial success of developers and publishers, enabling them to invest in future projects and support existing ones. The existence of unofficial versions can undermine this ecosystem. diablo 3 xci
Diablo 3 is a game designed for short, repeatable bursts of gameplay (Rifts, Bounties). For CFW users, loading an XCI means no installation is required in some setups (using SX OS or emulators like Ryujinx/Yuzu). You simply load the XCI file and play. The lack of installation lag makes it ideal for hopping in and out of Sanctuary. The Eternal Collection includes the Reaper of Souls
This is the format used for digital eShop titles. The existence of unofficial versions can undermine this