This wouldn't be very helpful, because someone might have e.g. offered a silly trade for every single one of the other person's pets, or sent a random trade offer that definitely won't be accepted. Having red text being displayed in this case doesn't really give you any useful information.
When it's showing your pets that you've offered in a trade that you sent it's helpful, because you know exactly what trades you've sent and what it means for one of your pets to already be offered.
