I have a hypothesis about what happened with Zillow. They started making offers on houses in limited markets in mid-2018. But they were never the only player in the "instant closing" game. There was OpenDoor and local cash "fast close" buyers to contend with, at a minimum. My area also had a very large volume real estate agent who was advertising heavily on billboards and the radio that he was in the "instant offer" business. So Zillow went into this pretty competitive environment with a tactical flaw: provide a high offer sight-unseen using their computer modeling, then lower it dramatically upon inspection even when a home had all systems functioning. It backfired, and so then they changed their offer strategy too fast, and now that has backfired.
Here is what happened when they made an offer on my home in mid-2019. The initial offer in the mail from Zillow was $300K. Okay, I'd been watching my local market closely for years and local realtors were telling me to list it at $290-$299K, so $300K with a fast close sounded good. I told Zillow come on by and do your inspection thing. My home had been kept up, had brand new hardiplank siding (less than two years), new roof (less than two years), new water heater, new appliances, neutral colors, light tones in the kitchen, trimmed landscaping, etc. The guy spent about an hour looking around my home, and then I get this high pressure sales phone call saying Zillow now estimated they were going to make $60K in "repairs" (things like replacing my perfectly fine white laminate counter tops, redoing ALL of the plumbing in the home even though there were no active leaks, etc.) So, the "revised" offer from Zillow is $240K. Totally absurd, but also totally high pressure. Umm, no, thanks. I'm not a distressed buyer, and this house is actually in really good shape.
Meanwhile, OpenDoor recognized they had a big new competitor and completely changed their strategy. The guy from OpenDoor came by that same week and said "We used to look for smaller things to repair or replace, but the strategy has changed and so now we're just here to measure, make sure your reports are accurate, and confirm that this isn't a dilapidated hoarder situation. I have been told that my job is to find nothing wrong unless there is REALLY something big wrong." Their initial offer was $283K and their "revised" offer after inspection was $283K. I was even able to get them to lower their "commission" bullshit by one percent due to the relatively new siding and roof. And they could close in 2 weeks, which meant I could turn around and close on the new home I wanted to buy without having to pull any cash out of my stash.
Obviously I sold to OpenDoor. They took the commission cut, did nothing to repair or improve the home, relisted it at $300K, and then sold it for $290K about 4 months later. As far as I'm concerned that was a win-win. They made a little money, and I made a fair sale but didn't have to deal with time on the market or flaky individual buyers and their laundry lists of issues.
I saw other "for sale" signs from OpenDoor pop up in yards here and there. I'm going to guess Zillow was not successfully purchasing anything in my neighborhood that first year. They were outwitted and outplayed by OpenDoor where I live, because OpenDoor had had boots on the ground for much longer and knew what they were doing in terms of the local market. So did Zillow then radically change their strategy in an effort to outbid places like OpenDoor? Sounds like it . . . and it backfired.