Let’s say you dig a 1x1m hole, which gives you enough room to wield a shovel. For each metre that you dig down, you have to remove a cubic metre of earth, weighing 1.6 tonnes. Even if you have some kind of bucket elevator so that you don’t need to lift the soil to the surface, you’re still shovelling almost 100 tonnes a minute.
Maybe instead of manual shovelling, all the digging is taken care of by an automatic drilling machine that you stand on. But for every 40m that you descend, the temperature will rise by 1ºC. After 33 minutes you are 2km deep, and you die of heatstroke in the 50ºC air.
Even if you have some kind of amazing cooling system, you are still in an ever-deepening hole with almost no fresh oxygen diffusing in through the narrow opening at the top. After a couple of hours of effectively rebreathing the same air, you’ll die of CO2 poisoning at a depth of 7km. Or whenever your bottled air runs out.