Green beans can taste bland due to the type of green beans being used, your cooking method and as a result of the lack of addition of flavors.
When fresh green beans are not cooked properly, the fresh green beans can lose their natural sweetness.
And canned green beans will also often have a bland flavor as a result of the canning process and the preservatives.
Overcooking the green beans can also cause your green beans to lose their natural sweetness and develop a mushy texture.
Simply boiling the green beans without adding seasonings or flavor enhancers can also result in bland green beans.
Also different green bean varieties also have different flavors.
For example, pole beans are know for having a stronger and more earthy flavor than bush beans do.
If you want to enhance the flavor of the bland green beans you can add some seasoning such as salt, pepper, garlic, onions or other herbs which help make the green beans taste much better.
And opting for recipes that have limited flavor additions like green bean casserole can also result in a bland green bean dish.
If you're using dried green beans, soaking the dried green beans in salted water before you cook them can also help to make the green beans rehydrate faster and enhance their flavor.
Canned green beans are often cooked in a salty brine or even sweet syrup which can also alter their natural flavor and some canned beans can take on the metallic taste of the can itself.
Fresh green beans tend to have the best flavor and texture when compared to canned green beans.
Also avoid overcooking the green beans and add flavor enhancers like onions, herbs, garlic, pepper and salt and choose fresh and high quality green beans.