When it was first changed we didn't get ammo in loot but the returns we so poor and enough people complained we got ammo as well.
Or, what happened was this:
At the VU when animal oils were implemented, all PEDs in ammo was replaced by animal oils - consider the typical drop of today but instead of the ammo, "animal oil residue". I didn't even notice the change the first day, because I thought the animal oil residue was the familiar PEC coins.
However, the problem was hunting in lootable pvp. Gettig animal oils and residue in lootable pvp would mean that you would lose more than Before if getting killed, so replacing animal oil residue with ammo was a way around it.
Another thing was that players were thinking if it shouldn't be possible to Craft ammo. Maybe as a response to that, the explosives got implemented, but so far they have only been in loot, they haven't been craftable.
The complaints about ammo in loot:
1) People who want to track their returns in hunting have it harder, especially if the base for the hunt is "I go out with 50 ped ammo, I shoot it up, and check my returns".
2) After a long:ish run, you tended to end up with a zillion stacks of ammo (too small for your gun to use). I guess the stacking algorithm is smarter now, and you only get new stacks when buying ammo. Also, today there is a "merge-all" function for stacks.