It's as equally pointless as female circumcision.
Alright but what if you're like hunting or in the military for a few months, hmm?
Most military camps have showers so you can clean yourself.
Furthermore, if you're out hunting for some time or are on a prolonged military operation (e.g; special forces) then the dirt you're most likely to accumulate will come from soil/mud and/or blood.
In that circumstance I would much rather have a hood around my snake to protect it. In this hypothetical situation you can't clean yourself, so having an ever so slightly more cleanable snake isn't a benefit, and having an exposed glans snake is a disadvantage.
And on top of all of this, the most common 'dirt' that accumulates around the snake and foreskin is sweat, urine (which is cleansing and mostly sterile) and smegma.
Smegma only accumulates if you're loveually exciting yourself or ejaculating, which you're probably not likely to be doing if you're out hunting or in the military away from a shower (or even just a fresh pool of water/stream).