I know you're more than likely a troll, but I'll answer your question since this is a question that is genuinely asked by some people.  It is simple. The Armenian Apostolic Church was part of the Catholic Church during the Church's early life; and Thaddaeus and Bartholomew were the first Bishops of Armenia - just like Peter was the first Bishop in Antioch and later Rome where he finally settled. Thaddaeus and Bartholomew were still under the authority of Peter. Centuries later at the Council of Chalcedon in 451, the first schism occurred by the Oriental Orthodox Church from the Catholic Church over Christ's Divine nature and human nature. The CC believes Christ's nature is fully human and fully Divine yet separate. The OO believe both nature's are fused together. If I am not mistaken, the AAC broke away from the CC over this issue, too, siding with the OO.

The OO Church's first Bishops were the Apostle Mark, who settled in Alexandria, Egypt; and the Apostle Phillip, who settled in Ethiopia to spread Christ's teachings. They were under the authority of Peter too, but centuries later, the subsequent Bishops of these lands disagreed over Christ's Divine and human natures which led to the first schism of the Church. These Churches still have the 7 Sacraments and Apostolic Succession, but few of them are in communion with Rome; and few of them affirm the Seat of Peter as infallible.  

...why is this Church not apart of the Catholic Church...?

They are apart