Anyway, the priest asked a question of the audience: Why was John the Baptist running around the wilderness, anyway? Why wasn't he at home or preaching in the middle of Jerusalem. His father, Zachariah, was a priest of the Temple, so it would've made sense for little John to have followed suit and made himself at home preaching to Jews in Jerusalem.
The priest answered that John was preaching in the wilderness due to the corruption of the Temple.
That is probably true, but it glosses over a HUGE reason of how little John found himself in the wilderness in the first place...
Everyone seems to forget that John the Baptist was only a few months older than his cousin, Jesus. The Blessed Mother visted Elizabeth, John's mother, when she, herself, was pregnant with Christ. That puts John about 4-6 months ahead of Jesus.
Anyway, if the Holy Family had to high-tail it away from Herod due to his desire to kill all young boys from birth to age 2, little John would've been a prime target, especially since he resided so close to Jerusalem (what with Daddy being a priest and all). As a result, little John was taken by his mother, St. Elizabeth, to the wilderness where she stayed with him until it was safe to return home.
However, the fact that little John escaped from the slaughter made many people very suspicious. Folks were angry and jealous that Zachariah had somehow managed to keep his son alive while theirs were cruelly murdered. They constantly would've been asking him "Where is little John? Where is that son of yours, Zachariah?" Off little John would've been sent to the caves once more to hide away until the anger passed.
John the Baptist was made quite at home in the wilderness in his early years. As Blessed Anne Catherine Emmerich wrote of him, nature was his school house. The birds, flowers, elements and grasses were God's own alphabet, and little John was a quick study. He was well acquainted with his guardian angel who was sure to teach him the finer points of what would soon become his Advent message.
So yes... while there was plenty of corruption within the Temple at the time of John's preaching, that was not "why he was in the wilderness." He was in the wilderness because from a very, VERY early age, he was forced to find refuge in the wild - away from hateful eyes, vice-filled souls, and yes, the corrupt teachings of the Temple.