Why do we see many worshippers characterized by the worst manners, even though the noble verse says: "Indeed, prayer prohibits immorality and wrongdoing"?

The true, accepted prayer restrains from indecency and evil, and in it are realized humility, presence of heart, and remembrance of Allah. So, for whoever these meanings are not established in their heart, their prayer will not yield the desired fruits, and they will not be written any reward from it except in proportion to what they achieved of its meanings and objectives. The prayer that influences a servant's conduct is that which is performed with humility and an awareness of Allah's greatness.