In the beginning of Perek Hakones, it cites Rebbi Yehudah's shita that a Tam needs a superior Shmeirah to be potur, however a Muad you will be Potur even with a lesser Shmira, Understood it is a Gezerias Hakosuv, is there also a Pshat in Sevarah?
Kol Tuv, Ari Stern
The Me'iri writes that the reason for this Halachah is that if an ox has gored 3 times and thereby has become a Mu'ad, this is a well-known fact and it follows that it is fitting that the public should be careful to avoid being damaged by such a Shor. Therefore, a lower level of Shemirah on the part of the owner is sufficient.
The Pnei Yehoshua (end of DH b'Gemara Amar Rav) writes similarly that the public have an oblgation to keep themselves and their animals far away from this Mu'ad. The result of this is that the Mu'ad does not damage so much, which is why it is sufficient to exercise a lower level of Shemirah.
Kol Tuv,
Dovid Bloom