Because this was a vault, the building was constructed extremely sturdily; not only that, although the vault couldn't be used as a bunker, it was definitely one of the most solid civilian buildings.
Gao Guang didn't know how thick the walls were, but he knew the wall was behind him, and unless the enemy could blow up the wall first, they wouldn't be able to attack him at the end of the corridor above the vault.
But the vault's wall wasn't made of brick—it was reinforced concrete, part of an integral frame structure, not so easily blown up.
The electronic jamming vehicle hadn't been used, and if they stubbornly defended the entrance to the vault, the jammer would fall into enemy hands.
To fly a drone, they would have to go outside the building, a move that would likely result in a sniper's bullet; even holding the drone out of a second-floor window was risky and might attract a sniper's attention, so even with a drone, it wasn't safe to use it.