Computing power, miniaturization and power density.
Graphic cards have come a long but they still have a ways to go before rendering graphics that are detailed enough to match reality.
Then there’s the ability to fit the existing graphic card capabilities into VR headsets. A high end graphic card is huge and can’t be fit into a headset.
Finally, there’s power density. Unless you want to have a cable running from the VR headset to the wall, you need a battery that can drive all the necessary power. Graphic rendering sucks up a lot of power.
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