I can tell you from experience of 2 crashes, 1990s and 2008, contrary to what people think, when an asset is crashing in price, investors do not pile in and buy. Property was a dirty word, and avoided. Problem is, no one knows where the bottom is? Purchasers hang back waiting for better value, and so the price continues to drop. No one wants to pile into a declining asset / catch a falling knife.
BTL Landlords and investors hit the wall first as they're usually over endebted, working on fine profit margins, paying higher rates than most residential loans, and the banks call in their loans a lot quicker than residential, as they have less duty to protect them.
Houses don't dissappear when BTL no longer rent them, and convert to residential instead. Giving those previous renters a chance at home ownership.