If you play more tables, your concentration decreases with each one. From the point of view of professional players, there are more chances to earn money without worrying about one failure.
You'll need maximum concentration if it's live poker and the buy-in is significant.
If you're playing online, all you need to do is beat the variance with the right strategy and a high volume of
hands. This can only be achieved by playing as many tables as possible.
Couple of 32" 4K monitors, a few weeks of practice, and 12-18 tables = easy!
You fold 70-93% of your hands, so it's rare that you're playing around six hands at a time. usually just 1 or 2. HM or PT collects the data for you. You can easily adjust bet sizes and ranges by sorting the tables on the screen or changing the colors. Keyboard shortcuts are an indispensable feature.
Good Luck!