If commercial reasons aren't behind this, then something else must be.
A mass kicking out doesn't happen for no reason, especially if there's going to be a major loss of income.
There appears to be no social reasons for this, nor is it common in that area.
There seems to be no laws governing this, nor discrimination against married and unmarried couples.
In fact, long term cohabiting couples seem to enjoy the same rights as legally married couples, suggesting no gender based rules regarding living anywhere they please.
The question is - what's happening and, if anything, is it just one building or all over the city?
There appears to be a massive glut of flats, but not even close to enough people wanting to rent them, so any such action by the owner would be extremely foolish.
Add the 10s of thousands of empty properties, either unsold or waiting to sell at a profit, and it's a buyer's market.
Nope - something else is happening here.