Because the hands are part of the viewmodel. The goop disappears because the other weapons are not gooped, and thus their viewmodels are not either.
He wipes his gloves when he reaches for another weapon? 
Limitation on the engine, I think. Oh well, has there been confirmation that a console command or convar can remove the splatters on the viewmodels? Or is this something inherent in the mod’s programming? If it’s the former and the command has been provided, I will close this thread. If it’s the latter, the developers know about it and will work on it to provide it as an option, and I will close this thread.
So, has a solution been reached?
There is a command for that: cl_mdldetailfx_enable 0
But it will also disable aliens being covered in blood as they die.
Well, it appears that until the developers implement the option to remove individual splatters from the viewmodels, the cl_mdldetailfx_enable 0 option is your best bet.
Hopefully that has helped you. I will close this thread as the question appears to have been answered.
Please use the Got a Question? - Enquiries About the Mod thread for questions like this in the future. Thank you.