Because you think it's difficult.

There is a truism (though not a "law" per se) called the Law of Attraction. It's that the world around you changes according to what you will of it. This is not saying everyone has reality-bending superpowers though, that would be absurd.

Say you wonder why is making money so hard. Earning money is basically getting value in exchange of the value you create, the foundation of modern-day capitalism. Is there anything you're doing that creates value? are you given value for the value you created? is there demand for your supply of value?

Sometimes all it takes is knowing the right customer to set you on the course of getting paid to do what you do.

Maybe you're a working salarymen and promotion is hard to come by. Well, do you have the value to warrant a promotion? have you gotten better as an employee since you started working? There are 24 hours in a day, 10 is for resting (ideally), 8 is spent in your workplace, what you are doing with the remaining 6?

Money is merely a means to an end, stored value, ultimately you have to first be clear with yourself of what your goals are. The pursuit of money is a path to madness and if you ask all the billionaires in the world, chasing money was never their end goals even though somehow day by day they get "magically" richer.