Wheel nuts too tight causing this exact issue is common on these. The flange that sticks off the back of the wheel can press hard on the inner race of the bearing and crush it. It causes the bearings to bind up.
When I bought my Treal wheel hexes this happened. I ground that flange down and it...
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The reason you can't turn the wheels is because the SCX24 uses a worm gear in the axle housing. Trying to turn a worm gear assembly from the output is next to impossible due to the design.
Are you having issues with operation? If so, check to see if your wheel nuts are too...