The disciples knew that the Pharisees, by their influence, could prove formidable enemies, so would have thought it prudent to conciliate them. The Pharisees had taken offense, because the doctrine of Christ was subversive of their traditional customs, regarding frequent washings.
The disciples of Jesus recognized that the Pharisees, due to their authority, could pose a considerable challenge, so they would have considered it prudent to try to win them over. The Pharisees were offended because Jesus' teachings conflicted with their traditional practices concerning purification rituals.