When Black Box decided to trade lives for lives, Gao Guang had no choice but to confront them.
Firepower couldn't provide coverage since the Russians' supporting firepower was now limited—long-range rocket artillery and missiles couldn't keep up, and the accuracy of the long-range rockets was insufficient. As for ground-to-ground missiles, multiple rounds would be over by the time targets were set.
Artillery support was unavailable; even if there were cannons, they were out of sight range. And out-of-sight-range artillery required guidance and adjustments, which would also take too long.
Infantry existed, but they were too far away. By the time enough infantry had gathered to form a superior force, Black Box would have retreated underground again.
The tanks had already been destroyed, and armored vehicle support was on its way, but "on its way" ultimately required time.