Coptic.net gives the following explanation:
“The Liturgy according to St. Basil is the one used most of the year;
St. Gregory's Liturgy is used during the feasts and on certain occasions;
only parts of St. Cyril's Liturgy are used nowadays.”
They also mention the following:
“It is worth noting here that the Liturgy was first used (orally) in Alexandria by St. Mark and that it was recorded in writing by St. Cyril I, the 24th Patriarch of the Coptic Orthodox Church of Egypt.
This is the Liturgy known as St. Cyril's Liturgy and from which the other two liturgies -- referred to above -- are derived.”
My question is:
If the St. Basil and St Gregory liturgies came from St. Cyril - why not just use St. Cyril’s liturgy all the time? It’s literally the liturgy that St. Mark used himself ... so why don’t we pray it that often?