John Gill Commentary Judges 17:8

"And the man departed out of the city, out of Beth-lehem-judah, to sojourn where he could find [a place], and he came to the hill-country of Ephraim to the house of Micah, as he journeyed." — Judges 17:8 (ASV)

And the man departed out of the city from Bethlehemjudah ,
to sojourn where he could find a place. Either being a man that had a rambling head, and of an unsettled mind, and could not easily fix anywhere; or else there being no supreme magistrate, to take care that the Levites had their due maintenance, for which there was a sufficient provision made by law; and the people being negligent of paying their tithes, there being none to oblige them to it, and they indifferent to the true worship of God, and prone to idolatry.

This man was obliged to go abroad, and seek for a livelihood where he could get it, and sojourn in a place the most convenient for him:

and he came to Mount Ephraim, to the house of Micah, as he journeyed :
Not with a design to stay there, but called by the way.

Having heard perhaps that Micah was both a wealthy and an hospitable man, and he also might have heard of the new form of worship he had set up in his house.