Because otherwise outputs go down, with people naturally making effort to do whatever it takes to qualify for the best compensation, rather than actually doing something productive (as high outputs is not it). As the result, the whole economy (and thus, society) struggles.
Check history of the Soviet Union - it was a glaring issue there.
Have you considered that in a discussion about the USA a modern Europe the Soviet Union might possibly be completely fucking irrelevant? But yeah, my bad, I keep being naive and assume that people try to interpret what I say in a reasonable manner instead of shouting COMMUNISM!! SOVIET UNION!!!
Which famously struggled because it didn't overpay its software engineers enough. So instead of doing productive work like optimizing ad impressions and creating DRM they all became garbage collectors and cleaners.
No, I'm not trying to engage in constructive debate right now. Apparently I lack whatever skill is needed to debate liberals without triggering their COMMIE!! reflex.
Please keep the discussion civil. I haven't said anything that you imply I had and no one called you a commie (or any other slur) or even used word "communism" at all.
I've just mentioned Soviet Union as prominent and well-documented example. Don't put words I haven't said in my mouth. Thank you.
Heck, this issue is not even specific to communism.
Check history of the Soviet Union - it was a glaring issue there.