Simply because there is no challenge in it and it doesn't force your reactions or make you struggle or take a hundred times just to barely win or to win. I have played a lot of them and they are literally no challenge at all, it may be great for strategy game loving people but for me it's too easy therefore not my cup of tea.
Iv always found turn based combat to be tougher then none turn based combat lol. I dont remember the last time i lost in a single player game that wasnt turn based.
Each his own it seems.