As we grow up we have learnt to be polite and we use words such as Sorry, Thank you, Please almost mechanically. When used mechanically words lose their meaning to the receiver because the receiver adjusts what you say based on their past experience with you.
If you are saying I love you, to your wife or significant other at every instance possible, there will be times when it is clearly mechanical and not meant as deeply as other times. Same way a person who apologizes casually reduces the impact of an apology. If you are selective in what you say and mean what you say as a habit your credibility goes up and people accept what you say.
Many people say things to avoid a conflict or to just avoid unpleasantness. Consistently doing so weakens the relationship and your ability to handle conflict in the future.
Say only what you mean and mean what you say deeply.