That is exactly the problem, the immense emptiness of Siberia. No roads, no accesses, no way to build a logistical network, no nothing. No way to get to those resource rich areas, even if the Japanese knew where they were (remember the Soviet paranoia about maps?). The only sensitive areas close to the border would be the Transsiberian railway (and the Japanese had once tried to go for that and got a bloody nose) and the Vladivostok (Primorskyi) Region but that was heavily fortified and manned. Good luck to them! All the rest was really quite far from the Manchurian border, on the East side of the Urals, thousands and thousands of miles away.

Actually the Russians did do exactly the converse in August 1945, that is, smash through Manchuria - also a damned barren land. But they did this in style: an overwhelming correlation of forces, highly trained armoured troops, doctrine to employ them that had been perfected against the toughest masters, imaginative logistics.

All that the Japanese lacked, the Russians had. They were just biding their time, waiting for a front to be finished before embarking on a second one.

__________________