What are randoms so stupid?

I'm so sick of randoms. Like ever couple of games you encounter players that won't share things like ammo , health and shields .

Usually I'm battling away and they are off looting. The will happily leave me with a slither of health, no shields or ammo.

I ask for it both on the mic and the ingame request. Players can literally see your low health bar. So I get I need enter a battle with no anno or whatever.

Selfish teammate usually goes down. If I don't die and manage to check my teammates death box out of curiosity just to see if they really did have an abundance of want I needed.

99.9% of the time they have massive stockpiles of EXACTLY what I needed and was asking for.

Can players really that selfish and stupid ? I just don't understand why you wouldn't want your team fully stocked so you have the best chance at winning engagements. It's lose lose for the whole team.

I just can't get my head around it ? A lot of the time I've had grown ass men shout down the mic because I couldn't help/ revive them because I had no health or ammo.

What gives?