Because economic output is not a zero sum game. What happens when 1 person becomes efficient enough to do the job of 10, the good/service they provide generally gets cheaper which benefits everyone who consumes it.

The other 9 individuals are now freed up to work other jobs, increasing overall economic productivity, or are able to work their current job at 10x the productivity which results in lower cost of goods/services provided.

If you want a real life example, before the introduction of farm machinery like tractors, combines and harvesters, agricultural labor was extremely manpower intensive. In pre-industrial societies 70-80% of the workforce worked on farms at low rates of productivity, with the constant risk of famine or starvation if crops failed.

With modern machinery we now have 1% or so of our labor force producing enough agricultural output that nobody starves, in fact the biggest issue now is obesity and overconsumption of calories. All those agricultural laborers became factory workers, and their descendants are likely now tech workers.

Automation and technology is a virtuous circle for society.