Fiat Bintulu: Litany of the Saints at All Saints Day?

The Litany of the Saints (Latin: Litaniæ Sanctorum) is a formal prayer of the Roman Catholic Church and Western Rite Orthodox communities. It is a prayer to the Triune God, which also includes invocations for the intercession of the Blessed Virgin Mary, the Angels and all the martyrs and saints upon whom Christianity was founded, and those recognised as saints through the subsequent history of the church. Following the invocation of the saints, the Litany concludes with a series of supplications to God to hear the prayers of the worshippers. It is most prominently sung during the Easter Vigil, All Saints' Day, and in the liturgy for conferring Holy Orders. (Source: Wikipedia)

"It is most prominently sung during the Easter Vigil, All Saints' Day, and in the liturgy for conferring Holy Orders."

Here is where it gets interesting:

There is no provision for the use of the Litany of the Saints within the Mass of All Saints. (It is not included as part of the All Saints Day mass in the Missal.)

The Litany was not used during the anticipated All Saints' Day mass on Saturday - yet it was used by some other parishes/in other countries. Which led me to wonder: 

Why is the Litany of Saints optional?

One reason afforded to me was that All Saints' Day is for ALL SAINTS known and unknown. If the Litany is used during this Solemnity, there may be some misconception that All Saints' Day is reserved for the well-known saints (named in the Litany) whereas those other saints (ie. all the other saints in heaven) not-named are forgotten.

But there is one part in the Litany that invokes "All you holy men and women, pray for us", which would include all the unknown saints so rightfully, there should not be any misconception.

Given the validity of both arguments, that might be why it is left optional...

Know of any other reason why it is optional? Do share in the comments.