In my locality, I believe the difference is explained in part by local policies that severely restrict new building and renovation of old buildings. You might

In my locality, I believe the difference is explained in part by local policies that severely restrict new building and renovation of old buildings. You might not expect such housing supply restrictions to cause land prices and rent prices to rise at different rates. But you would expect them both to rise. There may be real estate speculators investing on a momentum theory, but renters aren't willing to pay a premium based on the past trend in rental prices. This theory wouldn't support unbounded divergence between land and rent prices, but it would support some divergence consistent with what I've seen over the past few years.