Orders arrive faster than paperwork
A permanent change of station can give weeks rather than months. In that window a household has to decide whether to sell, rent or leave the house empty, and each of those is a different insurance position. Deciding under time pressure is when the policy gets forgotten entirely.
An empty house crosses the vacancy clause quickly
If the house sits unsold and unoccupied, most forms restrict cover after a stated period, with water damage and vandalism the first to go. That is precisely the period when nobody is there to notice a problem.
Renting it out needs the policy changed first
A homeowners policy does not become a landlord policy because circumstances changed. If tenants move in, the form has to change with them, and the time to arrange that is before the keys are handed over.