I agree. We use caps on most live actions and they are lot of fun. They make noise to lure thieves, big amounts are extremely impractical to handle, lot of fun appears when someone brings "forged" caps and especially they feel so much post-apo.
I understand the appeal they have in LARPs.
But in FOnline they don't make noise, big amouts are extremely practical to handle and they can't be forged.
Also I think in the wasteland nobody would use bottle caps as money because they have no real use besides that it's a small piece of cheap metal.
You meet someone on desert:
- Hey, nice pistol, how about I give you this bag of 300 bottle caps for it!
- ? ? ?
- What, you haven't heard? It's official wasteland money!
- Get out of here conman (or I shoot you).
That's how it would be in post-apo wasteland IMHO

(if you would actually take a minute to think about it)
And the idea that "technology to produce bottle caps has been lost" is ridiculous too, if people were actually accepting them, that would be the first thing to re-invent on wasteland.