Ok, so it's the same situation as like one should use a new address for each receiving for privacy.
Correct.
Nothing has changed.
Miner do decide for themselve which address they include as receipent from the coinbase transaction (the mining reward).
The easiest way is to build the block always the same way.
Most miner probably have their address 'hard coded' in their software running.
This way they don't have to pregenerate a bunch of addresses and don't have to fill the list of addresses again once it is going to 'get empty'.
While i can't say for sure why they use the same address for every block they mine.. i would assume it is because of convenience.