The Jatha was a group of Gursikhs who lived simple lives as householders who got together and did Kirtan.  They were not trained raagees, so they sang simple tunes.  Simple tunes are used so that even young children and beginners can sing Kirtan. Not everyone can become a skilled raag kirtani overnight and others don’t have time to learn due to other responsibilities, so simple tunes are those, which are based on raag, and can be learnt by all without much problem.

The tradition of simple tunes in panth has been there since the start.  Hence the tradition of Chaunkees and JoTeean shabads.  Same with Parbhaat Fayrees.  At Darbaar Sahib, at certain times in the day, the Sangat go in the parkarma and sing shabads together in simple tunes or JoTees.  This is a puraatan maryada and at certain times of the day it happens.  It happens at Bangla Sahib, Patna Sahib and other Gurdwaras too.  This maryada has carried on from puraatan (old) times.  At Nagar Keertans, a puraatan (old) tradition, sangat sings together in simple tunes.

Much of Gurbani has no raag whatsoever including Jap Jee Sahib along with many other Banis.  The main thing is to sing Gurbani with love.  Many Gursikhs such as Bhai Randhir Singh reached amazing spiritual heights by singing Gurbani in a simple but loving way.  Keertan sung with love by a keertanee who is connected to Vaheguru is most important.

Many prominent kirtanis in the Akhand Kirtani Jatha in the past such as Giani Amolak Singh were well-versed in raag Kirtan.  Even today, Kirtan done at AKJ programs and smagams is usually a mix of Kirtan done in simple tunes as well as Kirtan done in raag.