"Because of Jezebel"
In Revelation 2:20 - it says, "you allow that woman Jezebel"... whether her name was literally Jezebel or not doesn't matter. This woman most definitely has the same character of the Jezebel mentioned here in 1 Kings 21:25.
Ahab, in himself desired evil, but it was this woman, Jezebel who would stir it up and, shown in the Hebrew word, became the driving force that would carry out his evil desires. This means that, though King Ahab wanted to do evil, he would allow Jezebel to lead the way for him. We see this in many instances, such as:
1 Kings 18:4 - Though Ahab was King, it says Jezebel killed the prophets of God
1 Kings 19:1,2 - Ahab whines to Jezebel and she threatens Elijah, the prophet.
1 Kings 21:1-16 - Ahab whines again and Jezebel handles the situation in the name of the King.
Our flesh is always desiring against the will of God and I think we can all agree it is strong enough already without any help. So let's not give it help. We tend to bring people into our lives that seem to have the same weaknesses as we do; but we have to be very careful with whom we choose to spend our time with. A good question to ask is... Are they leading you to a closer relationship with your Lord and Savior or are they leading you away from the Lord and into compromise and worldliness?
It may be hard to end a long-lasting relationship with a close friend, but the Lord will bless us for the sacrifice we make so that we can have a deeper and closer relationship with our God. Remember the words of Paul, "I have suffered the loss of all things; and count them as rubbish, that I may gain Christ and be found in Him". Have you had to suffer the loss of a close relationship for the sake of Christ? How has your life changed because of it?