Excavators, bulldozers and other heavy machinery essentially do their job by pushing large amounts of material around.
Huge bulldozers shoving tons of rubble and crushing the gaps as they do so is not an effective way to save the people trapped in the pockets beneath.
You can’t just pile in and shift hundreds of tons of collapsed rubble without it moving underneath you, potentially killing anyone who’s surviving in a small pocket underneath.
Shifting literally dozens of tons of rubble upsets the balance of the whole pile, and you have people underneath. By hand, you can do it safely. By machine you have to be ultra-careful and risk collapsing the whole pile.
People can and do live for days in such scenarios, and it’s better to recover them safely than find out that you caused a collapse which killed someone who would have been relatively uninjured.
Also, what you want in those circumstances is SILENCE.
Every now and again you must ALL stop work, to listen for cries of survivors so you know where to focus your efforts, even if all you can do is reassure them or get water to them, it’ll extend their life by days, sometimes weeks.