That is how the market works and as technology gets older, please do not take offense when someone has to break to you the truth. And everything is used.

The 3900X goes for around $200 on here, Ram is around $150, Motherboard is around $200 and the GPU is around $700. Your GPU being a Liquid Devil is more more of a challenge to sell than anything else because it is a liquid cool card with a very niche crowd, when the vast majority of users are ones looking for either Air Cooled and/or hybrid AIO cooled. PSU lets say around $100, Case is $50, and your NVMe and SSD are around $100-150.

All your water cooling parts are considered a sunk cost to be honest because the number of water cool builder to regular builders are 10-1 if not maybe even less, which limits marketability even further.

And also take into account, full builds will often times sell for less than parted out because for more enthusiasts to this hobby, they would rather build it themselves than buy something already put together.