I’m not saying all landlords do so but what you described happens quite often. Landlords buy a property when they already have a place to live in and then rent out said property to someone who has none. And now said someone can’t own a property because there’s none on the market as all are bought out so all what is left to do for those people is to rent. It’s an oversimplification of course and there’s a lot of nuance to it but the general message still stands - if a person with a house buys another house to rent it out then one less house remains to be bought for people with no house.
And to add on the “the second the market opens” part - landlords can buy houses even before they are fully built and liveable which is not really an option for a person with no house because such an investment leaves you with no place to live and no money (mostly).