I don't think they are going for 100% or even 90% realism. Still I understand the gripe. It isn't a military simulator though.

With a little imagination though you can imagine that a special ops group wouldn't always have time to have new weapons and equipment dropped in any time they need new shit. A lot of them are expected to make use of their surroundings and enemy's weapons.

They teach snipers in the military to literally gather and tie sticks together with blades of grass/vine to use as a bipod for their rifle. Not uncommon to make entire hiding spots out of shrub and bush and stuff.

Also ammo runs out, weapons degrade/break, there isn't an unending supply of these things that can be given and transported to elite operatives any time they run out. Especially when your embedding inside the local militia and environment for long periods of time. If your goal was to build rapport with local militia and get them to cooperate with you, you'd be setting yourself apart if your getting special equipment given to you. Makes you that much more different from them.

I know it seems like that from anybody outside the military but they fully expect their soldiers to make due with what they have, unless it is fully justified to send more equipment, the higher ups will almost always avoid it.