הרי זה אומר מטמאיך לא טימאוני ואתה טימאתני
It says: that which made you tamei didn't make me tamei, but you are making me tamei!? [translation mine]
They all describe a situation in which A makes B tamei but cannot make C tamei, but B can make C tamei (and does, once B is tamei). This is surprising, hence (perhaps) worthy of remark.
However, does it need to be remarked upon (with the same language) nine times (and a further three in the tosefta) (and in fact several times in a row in Parah)? This personification language is unusual in the mishna (it seems to me), so why use it here? Is it simply a mnemonic/a common expression, or does it come to add something in particular to the halacha?