Because Latino's aren't automatically illegal immigrants - the group which I believe Trump was actually aiming at when piling them all in one stack under the name of 'bad hombres' and the like. I've heard somewhere (I think in a TV interview [with a sample of the Latino voting demographic]) that legal immigrants (especially Latino's) want illegal immigrants to be dealt with; since they've actually put in the work to earn their keep (or at least their legal status), when the latter mentioned haven't.
On the comparison with Romney I have no answer, as I am unaware of his campaign at the time.