10 Is max, more players would just kill the game... If you play poker for a longer time I think you would agree with me. I prefer to play 6max on cash game, it's faster and more skilled.
Think if 20 people sat on one table. They would rarely pay blinds and everyone would be waiting to hit some strong hand and nobody would play which kill the thinking game of poker.
If you try to play heads up tons of play is around
bluffing and exploiting your opponents weaknesses which is very fun.