NASCAR question about the Chase..

I am totally ignorant about nascar, so while this is probably an easy/obvious answer, please forgive me because I admit I'm not familiar with the topic.

With that said..what is the point of the "chase"? If I understand it right (which I might not), they race the season like normal, then at a certain point they basically just have a top 10, and only those guys matter anymore, is that right? If that is right, my main question is why the hell did it change? Back in the day they would just race the whole season and whoever accumulated the most points won, correct? So what prompted a move to the current system?