Lectionaries are collections of New Testament readings appointed for use during liturgical services. During each service there was (is still in some traditions) a Gospel reading from the Evangelion, and a reading from the Apostolos, which may be either an Epistle or a reading from Acts (but not Revelation). You will see these referred to as "Gospels" and "Apostles" in the list you linked.
The oldest manuscripts (again as shown in the article you linked) only date to the 9th century, but based on the writings of Church Fathers we believe the tradition dates back at least to the 4th century. Prior to that, the readings were chosen on a more ad hoc basis. The New Testament canon developed as a guide for which writings in circulation local churches should consider to be safe to choose from.
The development of the eastern lectionary is described at a high level in this article. The earliest form had readings just for Saturday and Sunday, with readings added for each day's Liturgy by around the 9th century.
The homilies on Scripture we have from Church Fathers are to a large extent sermons they gave for one or more readings that day out of the Lectionary. That certainly was the case for someone like John Chrysostom.
There is such a proliferation of lectionaries because until the printing press put books in reach of ordinary people, Scripture was heard rather than read and it was primarily heard during Church services.