Tiltbrush is opensource, but not actively being maintained by Google and hasn't been for a long time. Some of the original team is involved in maintaining an opensource fork, however, but this is not a Google product. Daydream was sunset a while ago and cardboard support has stopped also. VR is an interesting category for Google because there are often no services to maintain in VR apps. So, like an indie developer with a failed game, they can leave their VR apps on the Steam store with zero maintainence as long as SteamVR works. There are zero employees working on Google's VR apps except for Owlchemy, which I suspect is still around because they cost very little or they're profitable. Google Poly, which is a service related to VR, is getting shutdown.
As for VR not picking up, it didn't pick up on startup folks timeline but there has been steady growth in the market and it's close to sustainable for many developers. Facebook, Valve, Sony, Microsoft and Apple have been more persistent and came in with realistic expectations. I think this is a case where Google was premature entering the market and also premature exiting. If they re-enter they'll probably look like Microsoft trying to re-enter the mobile or tablet market in the 2010s after not succeeding in the 90s and 2000s. That's not to say that VR will "take over the world" like smartphones, but its on its way to evolving into a sustainable category with a variety of compelling use cases.