The Renaissance in 15th century Europe was, in my opinion, the first great change in how and why art was created. Combine the technological advances, such as oil paint, and the way the people began to change the way they thought the world to be, and a Renaissance (or "Rebirth") is bound to take place. This time period is the first we see a growing interest in Humanism. People began to wonder and observe things, all kinds of things, and take responsibility for their own existence. The general mass of people started to find out things for themselves, instead of believing everything that the church tells them.
I think there lies our answer as to why we have held on to the aesthetic values of the Renaissance for so long. Every generation since then has kept that same feeling of independence and knowing through observation, therefore prolonging, and advancing the same cause.
Also, just on a less heavy note, it is a beautiful time period for art. Master's of the Renaissance have "mastered" the use of perspective, value, and form, and capturing that "cinematic" feeling in a piece. For example, when we look at Michaelangelo's sculpture of David, we can feel the emotion that he captured in David's face and his demeanor. So, maybe for the longest time, artists are just trying to one-up each other in this movement, therefore things just get better and more precise and beautiful. After all, the art world in the Renaissance period was very competitive.
I personally subscribe to the first idea I proposed. We as humans are always searching for the "best" of anything, and definitely in art. We are always just carrying on and evolving what the Renaissance artists began.