[rodgerd]

> Why haven't bylaws been passed to curb this?

There were reasonably robust Adverse Possession laws in the UK, but they've been <a href="http://en.wikipedia.org/wiki/Squatting_in_England_and_Wales#... wound back</a> in favour of, surprise, surprise, absentee landlords.

Returning to the situation where owners who simply hoard vacant properties risk losing it to squatters would likely remedy much of the problem.