The Lord’s response to their question is entirely reasonable.
Firstly, it is essential to recognize the differing circumstances of these disciples. Secondly, one must understand how this practice aligns with other tenets of My teaching. Fasting is a manifestation of grief, a state in which thoughts of food are absent, stemming from sorrow for the loss of something. As long as I am with My disciples, they have no cause for mourning, similar to how the friends of the bridegroom celebrate while he is present. The disciples of John, however, can rightfully fast—practicing abstinence now that their bridegroom is not among them, as he is imprisoned. The Pharisees, who refuse to ally themselves with either John or Jesus, always seem to find reasons to fast; yet, in God's eyes, their fasting lacks the significance they wish to attribute to it.
When the time comes for My disciples to experience suffering, they will also engage in fasting, but even then, such a practice must harmonize with other external observances and their new internal calling. Simply mirroring the fasting practices of the disciples of John, which would involve modifying only one aspect of their lifestyle, is akin to sewing a new patch onto an old garment—a solution that only expands the tear. Likewise, imitating the Pharisees and adhering strictly to all previous forms would be like trying to store new wine in old wineskins—leading to the loss of both the new wine and the old skins.
Everything happens at its appointed time and within its proper measure. Thus, the Pharisees’ regulations, imposed upon Jesus, faced rejection, prompting the Lord's disciples to critically assess their relationship with both the Pharisees and the disciples of John, from whom some among them had originated. From this point onward, the scribes and Pharisees came to realize that Jesus was not inclined to conform to their opinions or regulations and intended to operate with full autonomy.