Getting ammo is too easy because of all the magazines that spawn in points of interest. Dense distribution of magazines attract survivors, who simply empty the mags just to get the ammo.

Examples:
7.62x51mmR is pretty rare in civilian area, so people will scrape military tents for SVD mag.
7.62x39mm - people look for AKM mags rather than boxes of ammo, because it's easier.
9mm parabellum - Main source is inarguably glock/CR75 mags, not the boxes of ammo.

In eloquence, filled magazines are disrupting healthy distribution of bullets. Magazines are surely a necessity, but they are making it way too easy to get ample amount of ammo.

Spawn more bullets, and empty the magazines.