Why some items can't be used for brush and turn them into skin?

[Keanu 61]

Basically tried White tiger's claw and Xmas crossbow, they are useless if they can't be used for costume or is there any reason why it can't be made for costume?

[jcompher 238]

I was hoping I could turn my xmas wand into a weapon skin with the paintbrush too but I think thats because they are special event weapons and you can get the xmas crossbow skin from the weapon crate, you just have to have really good luck... makes it way more rare.  its like cheating using the brush to turn the regular xmas crossbow into the skin without opening a ton of weapon crates and just using a paintbrush.

 

they are pretty useless on characters you are fighting with as normal weapons but i use them on my mules for looks.  just to have them.  they are like collectors items.  like the guitar and the wrench.