Commentary for I Kings 15:14

[However] the [private] altars he did not remove. The private altars upon which they had become accustomed to sacrifice to Heaven since Shiloh had been destroyed until the Beis [Hamikdosh] was built, when private altars were permissible, were not removed now, even though they were forbidden once the Beis [Hamikdosh] was built, and they were punished by premature death because of it.