Well the thing is that they still have to compete the energy transfer capabilities of a copper wire, so for a 2m long 1.5mm2 power cord, it has a round trip resistance of 40mOhm. If you use the worst case american 110V you can transfer 100W of power while creating 40mW of loss along the way. So the trusty power cord does its job with the efficiency of 99.96%
So even with the 70% efficiency that means you are wasting 75000% more power compared to a power cord.
Then bring a large metal object near the energy transfer area and watch the power consumption rise 2x 3x or even more as it is now doing a better job at being an inductive room heater rather than a energy transfer device. You can see that demonstrated nicely if you slide a flat metal object under a phone that is wirelessly charging, the thing becomes really hot (before the electronics realize power is going missing and shut it off to prevent a fire hazard)
But then again does anyone care if there TV is 50mm thick or 10mm thick? When it is flat against a wall anyway? Well TV manufacturers sure seam to have found out they do because it is the next big thing now that they all figured out how to do thin bezels.