‘And they said to him, “The disciples of John fast often, and make supplications, likewise also the disciples of the Pharisees, But yours eat and drink.” '
The complaint is brought by ‘they' who are unidentified. They may be puzzled onlookers or critical opponents. Their problem is that while both the disciples of John and of the Pharisees regularly fast, and make supplications, this is not true of His own disciples. They rather eat and drink. This last links with the feasting in the previous passage. But the question is concerned with whether His disciples have the right attitude to spiritual things. Is it not right to fast?
We know that the Pharisees encouraged twice a week fasting (Luke 18:12) on Mondays and Thursdays, and may presume that John's disciples did similarly, although not necessarily on the same days. The purpose of such fasting was linked with mourning because the Kingly Rule of God had not yet come, and probably in the case of John's disciples because he was in prison. The ‘supplications' would be in order to put right what was wrong, and now that Jesus was here would be no longer necessary. They would be replaced by new supplications as given in the Lord's prayer.
‘The disciples of the Pharisees.' This is shorthand for the disciples of the Pharisaic Rabbis/Scribes (there were also Sadducean Scribes) who were the Pharisaic equivalent of John.