Albert Barnes Commentary 1 Samuel 7:2

"And it came to pass, from the day that the ark abode in Kiriath-jearim, that the time was long; for it was twenty years: and all the house of Israel lamented after Jehovah." — 1 Samuel 7:2 (ASV)

And all the house of Israel lamented ... - The occupation of the country around Shiloh by the Philistines was one reason the ark was kept for so long at Kiriath-jearim. A further reason, however, appears to have been the Israelites’ fall into idolatry. This sin caused them to neglect the ark and brought upon them servitude to the Philistines—likely the last twenty years of the oppression described in Judges 13:1, which is explicitly connected with their idolatry.

Now, likely through the exhortations of Samuel, coupled with the chastening of the Philistine yoke, the Israelites repented and returned to the God of their fathers (1 Samuel 7:3).