Here is why. DUMB goals can give you the maximum growth opportunities while SMART goals can't. The true reward is not achieving the goal itself but the growth you get along the way.
The problem with SMART goals is 'attainable'. Once you start thinking about something attainable, you actually kill your opportunities for growth. When you set higher goals, you will know that you can do much more than you used to think. That's growth and that's the real reward of setting goals, the purpose of goal setting.
What is S.M.A.R.T. goals?
Are DUMB Goals Better Than SMART Goals?