It's nothing to do with power efficiently IMO.

Until energy storage gets dense enough to power these things durably, dependably, not happening. Did you see how awkward these things are? The standing/sitting transition is absolutely terrible and liable to cause pain or exacerbate a condition by being herky-jerky with fragile situations. They require active balancing, not passive. The first power glitch and someone may end up in a nasty fall or worse.

That's why I said supplement. There will likely be use cases galore. But there will be just as many if not more reasons to use something wheeled.