Prolonged sales cycles remove liquidity from the markets and generally restrict economic mobility of the population at large, as one needs to sell their current house in order to shop for a new one.
On the buying side having a no-haggle buying experience is also somewhat appealing to modern buyer https://www.opendoor.com/homes
The real estate is currently financed via debt instruments, and issuing debt for a real estate potfolio purchases is a fairly well-travelled path for many financial institutions and investors out there. OpenDoor is likely to spin that out as a short-term residential holding REIT, for better tax treatment, if nothing else.
Macroeconomic risk is always a factor with real estate investments, but the exit options are also well-known. Liquidate at any price, convert it to rentals, or wait it out.