The reasons that compost piles get warmer and hotter is due to the activity of numerous organisms breaking down organic matter.
As the organic matter breaks down due to the organisms the compost piles heat up and get warmer which is a good thing and when your compost pile gets warmer it's a good sign that the compost is working properly.
When your compost pile is doing it's job and getting hot enough the compost pile can reach at least 130°F in temperature which is a good thing.
If the compost pile is not getting hot enough then the compost pile is likely not doing good and you need to be sure to turn the compost over and don't put the wrong things in the compost pile which can affect it as well.