I think it's been well-known in the industry since the early days of VR that people don't like clunky headsets. But it's not like you can just will into existence a small, lightweight, standalone headset that delivers a smooth VR experience. There are hard technical problems to solve: inside-out tracking, battery life, heat management, optics, etc. The Oculus Quest is a step on the way there, but even after spending billions of dollars, they still have a long way to go.
The problem with lightweight AR is that with current technology, it's not that useful. If you've ever tried Google Glass or Focals by North, there's not much you can do with them that couldn't be done better with a smartwatch [1].
And if you try to pack a larger FOV display or more processing power into the glasses, you end up with something like HoloLens, and then you've got a similar problem to the VR headsets -- it's probably not something that you'll want to wear for long periods of time (you can't anyway due to battery life), and certainly not something you'd wear walking down the street.
It's not that these are missed opportunities. On the contrary, there are a lot of people who have been working on them for years with billions of dollars spent in the process. But they're hard, and it will take time to get there.
---
[1] The one exception was being able to capture quick moments with the Glass camera -- but of course, that raised privacy concerns.