That's because the game is already balanced. If you haven't noticed, CSAT forces spawns without body armor, NATO in the contrary has a bunch of thick body armor, that way what NATO wears as protection on their vests is the same as the armor of the CSAT uniforms.
Plus, it's a part of the scenario, CSAT gear is more futuristic than NATO's, they have a ventilation system in their headgear and uniform, that way it explains why their uniforms are more protected than NATO ones.

A NATO unit in body armor and a CSAT unit without body armor will have the same amount of protection. So if you play PvE CSAT won't spawn with armor vests, if you play PvP, desactivate the body armors for the CSAT team.

Cheers ! =)

I don't think you're balanced in the head :) steel plated vest is weaker then a piece of clothing, if you think this is balanced, then your a troll or a kid with down syndrome.

CSAT Uniforms have an armour layer under their BDU, you can see part of it on their forearm region, whether you think that's realistic or not is irrelevant, that's the setting. Thus it's not a bug.

And you should refrain from implying someone is mentally ill or "a kid with down syndrome" simply for answering your question, it's a great way to get banned.

I vote up because i don't think balancing bodies / uniforms along with sides is a good consistent solution.
Armor bodies should be the same for all AIs, until you want to demonstrate a human side superiority...
Then, uniforms armor could be reliable with their usage. It's totally weird to have a wet suit (CSAT) much more armored than any BLUFOR suit.
Many addons (not always under BI responsibility) reproduce these weird fittings. And furthermore, some scripters, as I am, didn't figure they can't mix Blufor bodies with CSAT uniforms, or OPFOR bodies with BLUFOR uniforms without unexpected consequences.

thegodfather issued a real problem in a bad manner but I can't imagine there is no consistent solution rather this poor patch-up job, unworthy with outstanding BI developments.

I also see this issue as a problem of balancing. Playing lot on EUTW PvP servers and one reason Opfor is winning more is just because their protective uniform. This kind of setup just gives too much advantage to Opfor with all over body armor protection. I would like to see protection not coming from uniform, but from different vests. This helps guys like EUTW devs to handle balance better. Now you just have to put this protective uniform on Opfor players and balance is gone. I like asymmetrical warfare, but in this very basic like uniform is just not working on PvP.

Some testing:
https://www.youtube.com/watch?v=3ZsqTFd8PWo
https://www.youtube.com/watch?v=MorAkWAx-Bk

Obviously this is a (questionable) design decision by Bohemia, who expect CSAT to be pitted against enemies wearing Carrier Lites. But, the real problem here is that many people, including mod devs, may not be aware that the CSAT unis have armor while those from other factions have none. On top of that, players who do know about it will actively seek to play on the Opfor team so they can benefit from this advantage.

The way I solved this problem is by making Opfor players spawn with the Officer Fatigues (U_O_OfficerUniform_ocamo), which has no armor, instead of the default fatigues (U_O_CombatUniform_ocamo). It looks slightly weird, but it sure does the job.

It should also be noted that the CSAT ghillies have extra armor too. Another weird thing I observed is that some Opfor guerilla uniforms (U_OG_*) also appear to have armor, while their identical counterparts for other sides have none, which truly makes no sense.