Both investors buying up homes and i-got-mine retirees can be part of the problem. They aren't mutually exclusive. One puts pressure on existing stock and the other ensures there's no new stock.
If you get involved with any of this on the ground, it's not really a 'both' question. It's the NIMBYism. Without that, you build enough for it to become not a very interesting investment and large-scale investors go find something else to put money in.
