In Australia most of the narrative on the housing affordability crisis is around lack of supply and nimbyism. In the meantime Melbourne has dropped to 4th most expensive city in the country and becoming more affordable. Most likely reason - land tax change in that state which is turning off accumulating multiple properties through investment and investors turning to other states where prices are still going up. So, while supply is relevant, I would say it is investor demand that is driving prices up.
This reverses causation. Investors are involved because prices are going up, not the other way around.
"Investors buying up housing" is a common explanation alongside "short term rentals taking over" but neither make up a large enough portion of the demand to explain prices.
I don't know what's so hard to understand about the idea that prices are high because the people who have the most influence over the prices want the prices high.
It’s not a coincidence that many abundists see nothing wrong with rent-seeking. They’re incentivized by it. Rent-seeking has corrupted market forces. Mao 2.0 will arrive eventually.