(Compare with I Kings 12:28-33.) There are at least two reasons why Jeroboam did what he did. One is because he had no choice. It could have been that the Levites stood up to him and refused to teach and participate in error, so they simply left. If Jeroboam wanted to institute a religion, he had to have priests. He could not use the Levites because they were none available. He decided, then, to install anybody in that position who wanted to be a priest.
The second reason is that he may have summarily kicked them out because they represented too much of a threat. What occurred, though, insured that there would be no one who knew God's way enough to be a threat.
Related to the leaving of the Levites, Jeroboam instituted his own feast—one very similar to the Feast of Tabernacles only exactly one month later. He gave the people something new to celebrate.
Again, the appeal of his changes was convenience. The law say that three times a year all the males were to appear before the Lord, and that meant traveling to Jerusalem. So, to the Israelistes, Jeroboam's reasoning sounded good. Jerusalem was too far. In addition, being a bit further north than the Jews, their harvest season was a little bit later than in Judea, and thus the Feast of Tabernacles represented more of a financial risk for them. They decided, then, "Why not have it a month later?" Can we not see the carnal mind working?
"Yeah, that sounds really logical. It's a good and practical change because now the Feast will never fall during the harvest season, and we won't have to worry about losing our crops while we're keeping the Feast."
"Wow, what wisdom! Why didn't we think of this before? Jeroboam, you're a real leader."
John W. Ritenbaugh
The Sin of Self-Deception