The Hydroponic has the combination of age and visual quality that collector skins need to hold value long term. It came out during an era where skin design was still finding its direction and that generation of AK skins feels different to everything that followed. Wear variations produce really distinct looks which adds another layer for serious collectors. Read through https://bleedingfool.com/gaming/why-the-ak-hydroponic-is-a-legendary-collectors-item/ recently and it covers the history and collector appeal well. Good read if you want to understand why this one keeps coming up in collection discussions