That there is a lot of it lying around, and that rear-area troops who have almost no chance of seeing combat still need some kind of weapon, so you might as well give them an absurdly obsolete weapon that is effectively free.
Seriously, you have to be in a very, very extreme situation to want to use a Mosin on a modern battlefield. They're being used in the LPR and DPR because they can't get enough modern assault rifles to equip their rear area troops. That's the only reason.
That there is a lot of it lying around, and that rear-area troops who have almost no chance of seeing combat still need some kind of weapon, so you might as well give them an absurdly obsolete weapon that is effectively free.
Seriously, you have to be in a very, very extreme situation to want to use a Mosin on a modern battlefield. They're being used in the LPR and DPR because they can't get enough modern assault rifles to equip their rear area troops. That's the only reason.