I can understand that, but I would ask you to write to the creator of the Avatar mod about this. If he has used high resolution raw material, he will be able to create much better HD textures than I can with upscaling.
I also see other problems in the future if I start creating HD textures for other mods.
Firstly, I don't want to use other modders' textures without their permission.
Secondly, if I started doing this, I would get a lot of requests to do it for other mods as well.
Thirdly, I would have to continue to support these HD mods.
All of this is a huge time commitment, far beyond my capabilities.
If other modders are interested in including HD textures as an option in their own mod, they can contact me via the Factorio Discord server and I will be happy to support them.