Note: The following question is for those who have a relative understanding of the following incident in Tanach. If you think you can help answer my question but need the necessary background I embedded the links that will take you to material discussed (Via Sefaria). Thanks in advance!
In regard to the incident of the פסל מיכה in Sefer Shoftim (See פרקים י"ז-י"ח), one of the last verses (the second last, to be exact) in פרק י"ח reads:
וַיָּקִ֧ימוּ לָהֶ֛ם בְּנֵי־דָ֖ן אֶת־הַפָּ֑סֶל וִ֠יהוֹנָתָן בֶּן־גֵּרְשֹׁ֨ם בֶּן־מְנַשֶּׁ֜ה ה֣וּא וּבָנָ֗יו הָי֤וּ כֹהֲנִים֙ לְשֵׁ֣בֶט הַדָּנִ֔י עַד־י֖וֹם גְּל֥וֹת הָאָֽרֶץ׃
The Danites set up the sculptured image for themselves; and Jonathan son of Gershom son of Manasseh, and his descendants, served as priests to the Danite tribe until the land went into exile.
Rashi elaborates that שבט דן continued this idolatrous practice until the first exile of Sancheireb.
If it is said of Kings like Chizkiyahu (and presumably even before then [i.e. David and Shlomo]) who cleansed the land of all idol worship, how could have this continued?
Is possible to say that Laish (or Leshem)-The land which the Danites conquered in that incident- was not a part of Eretz Yisrael? If so how could the claim be that the Danites worshiped idolatry until the exile of Sancheireb despite the implication of other times in Tanach that the Jewish kings were able to totally cleanse the land of it?