Because the mailman will probably step on it before it gets to you and to actually use the stuff you will have to lick the envelope, or just smell the rest of your mail, just like the previous hot sauce offer. This isn't worth it, the chances of you getting it where it hasn't been opened isn't good.
I mean if Taco Bell were offering free Fire sauce to send you in the mail would you really get it to get a packet? Not really worth it in my opinion.