At the end of the day, the biggest issue with the Mariners is that they are trying to compete with a payroll that is about the same as the Brewers. They have done a good job at building a strong minor league system particularly on the pitching side. But they throw around money more freely than the Brewers and the result is that they have been stuck with some bad contracts and they don't have the payroll to spend out of it.
If you follow Mariners fan threads, the common theme that you will see is cheap ownership, as they have consistently ranked as the most profitable franchise over the last several years and have made the decision to not increase payroll during the current competitive window. It sucks.