Because no communist country has ever succeeded in being materially productive, due to simple human nature. Once you put in place the same pay for everyone, the lazy and slackers realize they can get paid the same amount no matter how little they do, and the hard workers get tired of getting paid the same as the slackers for much more effort and give up trying. Productivity falls precipitously. This is what made the labor camps necessary—the country couldn't produce what society needed and had to force political prisoners to do all of the hard work people were unwilling to do with a guaranteed salary.
The result is deprivation with limited resources for everyone, the fate of every communist country, without exception. Yes, under communism everyone (except those with privilege) gets the same—deprivation. The misery is shared equitably.
While capitalism results in considerable disparities, there is far more to go around for everyone and even the poor under capitalism have as much as the average person has under communism.