Because the 99% agreement he has with the Church outweighs considerably the 1% where he may be in conflict. Like you said, he wasn't infallible and we don't treat him or any other Father as such.
You throw Augustine in our face because he says that Scripture has paramount authority(could you give me the reference again. Don't want to have to delve back over a 1000+ posts to find it) and then think that it will cause us Catholics to tremble. Yet he believed in the authority of Apostolic Tradition, the authority of the visable Church to bind the conscience of a believer, infant baptism, the Real Presence of Christ in the Eucharist, the Sacrafice of the Mass, prayers for the dead, Mary's sinlessness, Apostolic succession, the seven Sacraments, the canonical authority of the so-called "Apocrypha", etc... The list goes on and on and on...
How can a man who believes that Scripture is of paramount authority believe in such supposed unscriptural, indeed, it is said by some, anti-Scriptural nonsense? Unless, of course, it is the case that what paramount authority means to Augustine is not the meaning which you are trying to foist upon him.
Augustine is not the trump card you think he is. It would be appriciated if you would stop trying to use him as such.
Pray for John Paul II