Probably because I wasn't aware of such a thing. Where would you go to buy one of those? I see some on the Net but they don't say how long the cord is which is a key issue. Cordless would be even better...
Get a clip-mike or a collar-mike.
I used to have a nice Sennheiser collar mike (until I broke it). Was great for taunting my housemates when playing AoE, and it had the benefit that the mike didn't get in the way of your mouth when drinking beer :wink:
If the cable is too short, just get an extension cable - they're dirt cheap.