Albert Barnes Commentary Leviticus 25:30

"And if it be not redeemed within the space of a full year, then the house that is in the walled city shall be made sure in perpetuity to him that bought it, throughout his generations: it shall not go out in the jubilee." — Leviticus 25:30 (ASV)

Not go out - Because most of the houses in cities were occupied by artisans and traders whose wealth did not consist in lands.