It makes sense that Julius left the VK behind in context. the way I interpret it is Castlevania itself is a 'Creature of Chaos', which exists in both the astral and physical realms, so to speak. Leaving it in there is like stuffing bulbs of garlic into an ordinary vampire's open wound.
@ Plottwist The VK was used to destroy Dracula completely, so while the Japanese translation is subtly different, the VK being "used to separate Dracula's soul from his magical power" sounds to be referring to the final battle mores o than the act of leaving the VK behind.
This actually came up in a topic I posted in 2015.
https://castlevaniadungeon.net/forums/index.php?topic=8229.0Again, thanks to Plottwist for pointing out Julius' character description in DoS:
Julius Belmont:
A descendant of a clan of vampire hunters, he wields a generations-old whip named "Vampire Killer." He lost his memory when he defeated Dracula in 1999, and only regained it during last year's incident. He now assists the Church in their undertakings."When he defeated Dracula" is still arbitrary, but it gives a much better understanding or timeframe of when/why this occurred.
The most straight forward response as to why is that the Hakuba Ritual potentially merged both the VK's Memory to Julius' memory.. Since we aren't privy to the inner workings of the Hakuba Ritual, the world may never know.
I interpret Julius destroying Dracula, sealing the VK into the throne room where Dracula resurrects (maybe in the coffin/ altar itself) and then fleeing the Castle. When the window between astral and physical realms had shut and Castlevania was completely removed from the physical world, Julius' mind was so strongly interwoven with it that it blanked.. In AoS he mentions something to the effect of awakening in the hospital and not remembering his name which is why he goes by "J", he also mentions whenever he hears the name 'Dracula' he has a negative reaction.
Whether it was a byproduct of the ritual to preserve the identity and future lineage of the Belmonts isn't clear, but the memory loss appears to not be intentional imo. It seems more circumstantial to both defeating Dracula and being separated from the VK.