One must put these reasons together to explain why John left out parables. First the Gospel of John was written after the synoptic gospels. Some evidence for this is only the Gospel of John mentions Peter by name as cutting off the ear of the high priest’s servant. The speculation is that Peter was alive when the synoptics were written, and his name was left out to protect him. Another is that the synoptics leave out the account of Lazarus being raised from the dead. The speculation is that this was also to protect Lazarus. If John wrote his gospel after their deaths, then they no longer needed protection.
A second reason is John’s Gospel is about as long as what’s practical to write on a scroll, and he avoided repeating what was in the synoptics as if he expected his readers to already be familiar with them. When John did repeat accounts, he seemed to do so to include details left out of the synoptics. Note John 20:30-31 in ESV:” Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.” Also note John 21:25 in ESV, “Now there are also many other things that Jesus did. Were every one of them to be written, I suppose that the world itself could not contain the books that would be written.”
Thus, the best guess as to why John didn’t include any parables in his gospel is that John thought the parables in the synoptics sufficient and didn’t see the need to include any more.