Something is off with the difficulty selection in that "hard" in the easiest mode to play for a long time in. By only using 3 columns when at all possible and always leaving as many different colors and numbers open in each end of each column when columns can't be completed before re-rolling, I've been able to play for long enough on hard that I'm starting to lose interest.
The times the game is interesting is when I can't follow a simple strategy so I actually have to think about the situation. But right now those situations are too rare. Also, since it doesn't feel like there's inevitability in the game ramping up in difficulty, the game just feels like it's getting same-y. The board state after placing 10 dice and after 300 dice is pretty much the same. To keep me interested there would need to be some sort of complication(s) added as the game goes on.