Why doesn't the Orthodox church consider Saint Augustine Doctor and Father?

I think the simplest answer, which Ken Graham alluded to, is that we have no such title in the Orthodox Church. In fact, although the Wikipedia article cited is entitled "List of Eastern Orthodox saint titles", I would call these appellations instead of titles. There is no process for deciding, for example, who should be called a "Confessor" and who should be called an "Enlightener". As strange as it seems, in most cases people started appending these descriptions somewhat spontaneously and they simply grew into common usage. The Orthodox Church is very precise in most things, but thoroughly spontaneous in others.

This is tangential to your question, but Augustine, though considered a Church Father, would not be considered a "Doctor" of the Church in the Roman Catholic source of the word. Some of Augustine's beliefs are considered somewhat heretical, especially some of his early teachings on the relationship of grace, free will, and predestination.

Although Augustine expressed his opinions as theologoumena - theological opinions - and even renounced them later, some of them persisted in the west and are now foundational doctrine for many Christians.

Most cite the supposed dispute over Papal supremacy in 1054 as the primary reason why Rome and the East mutually separated, but there are also profound differences in theology - some stemming from how Augustine's teachings were interpreted - that preclude any kind of a reunion.

Augustine is found on the calendar of saints of the Orthodox Church, although some of his teachings are viewed as simply theological opinion, and these are generally rejected by the Orthodox Church.

For further reading, see Father Seraphim Rose, The Place of Blessed Augustine in the Orthodox Church, from Saint Herman Press.

Here is the short version of the answer:

The Orthodox church believes that Augustine gave a personal tint to his theology, thus deviating from the rest of the earlier patristic fathers, especially regarding the Trinity and the nature of sin and grace. The Orthodox think Augustine was greatly influenced by neo-platonism, thus he is more "philosophical" than the Eastern way of ascetism, sacramental and liturgical lifestyle.

To quote from Archimandrite Sergius Bowyer in his book Acquiring the Mind of Christ:

It might be said that one of the foremost difficulties with Augustine's thought is that he maintained a neoplatonist approach to understanding both God and human nature, which is based thoroughly on man's reasoning and rational abilities...This is what essentially separates Augustine from the Eastern Orthodox tradition. His approach is based more on philosophical concepts rather than on the experiential methodology inherited from the Church Fathers before him.

There is a certain amount of freedom within the various Christian Churches to employ or ascribe certain titles to particular saints or blessed in their own way (or traditions).

The title of Doctor of the Church was first instituted officially on September 20, 1295 by pope Boniface XIII, when he accorded this title to four saints, Pope Gregory the Great being the first.

"The Doctors of the Church are great saints known for their defense and explanation of the truths of the Catholic Faith. The original eight Doctors of the Church—four Western (Saint Ambrose, Saint Augustine, Pope Saint Gregory the Great, and Saint Jerome) and four Eastern (Saint Athanasius, Saint Basil the Great, St. Gregory Nazianzen, and St. John Chrysostom)—were named by acclamation, or common acknowledgment; the rest have been named by various popes, starting with the addition of St. Thomas Aquinas to the list by Pope Saint Pius V in 1568."

Even within the Catholic Church, various local churches and Rites have added their own saints to the official Catholic list of 34 Doctors of the Church. If this freedom exists in the Catholic Church, it follows then that other denominations have the same freedom!

"In addition, some parts of the Roman Catholic Church have recognized other individuals with this title. In Spain, Fulgentius of Ruspe and Leander of Seville have been recognized with this title. The Syro-Malabar Catholic Church has recognized Ambrose, Jerome, Gregory the Great, Augustine, Athanasius, Basil, Gregory of Nazianzus, and John Chrysostom, as well as Ephrem the Syrian, Isaac the Elder, Pope Leo I, John of Damascus, Cyril of Alexandria, Cyril of Jerusalem, Epiphanius of Salamis, and Gregory of Nyssa. The Chaldean Catholic Church has recognized Polycarp, Eustathius of Antioch, Meletius, Alexander of Jerusalem, Athanasius, Basil, Cyril of Alexandria, Gregory of Nazianzus, Gregory of Nyssa, John Chrysostom, Fravitta of Constantinople, Ephrem the Syrian, Jacob of Nisibis, James of Serug, Isaac of Armenia, Isaac of Nineve, and Maruthas."

As for the Eastern Orthodox Churches:

"The Eastern Orthodox Churches honors many of the pre-schismatic saints as well, but the application of the term Doctor or Father of the Church is somewhat more flexible than in the West, and it is misleading to look for lists of officially recognized Doctors. An Eastern Orthodox understanding of such pillars of the Church include saints such as Photios I of Constantinople, Gregory Palamas, Nicodemus the Hagiorite, and possibly even more recent saints such as Nektarios Kefalas. An exception to this flexibility is the grouping of Basil the Great, Gregory of Nazianzus, and John Chrysostom, universal teachers or Doctors who are collectively known as the "Three Hierarchs" and represent the Christianization of the Hellenic tradition and education."

The Eastern Orthodox uses various other titles that other denominations generally do not invoke for their saints. Their traditions remain quite valid.