I have flown for most of the major operators and many of the smaller ones and never have I been assigned my own life jacket. Either they have been hanging on a rack or assigned to an airframe. I currently fly SAR and we use Mark 44's with STASS. These are also not assigned to individuals - just airframes.
I have no problem with this as, unlike the comparison with helmets, they are not worn next to the skin. Seems a bit overly-sensitive to me to object to this policy. If this is an issue then what about sweaty seat covers and sweaty flying controls?