Why is exercise so important anyway?

Many benefits. Exercise has many benefits: 1) improved heart health and lower risk for heart disease (heart attacks,) 2) improved brain health (via adrenaline and endorphin release), 3) lower risk for stroke, diabetes, high blood pressure, and certain cancers, 4) improved cholesterol and blood sugar levels, 5) improved self-esteem, 6) improved lung function. Etc. Etc. The benefits are too many to list here.
Many reasons. Exercise helps keep body weight down. This improves our cholesterol scores and heart health. Exercise helps regulate blood sugar, which helps minimize the risk of developing diabetes. Exercise helps regulate blood pressure, which helps minimize the risk of stroke. Those are just a few of the benefits, but are very important ones.