Hi Jackie. Every time a soundwave crosses another soundwave, there is interference. Interference can re-enforce, but on average the soundwaves will cancel out. Additionally, the energy gets transfered to anything the soundwave passes through or reflects off. Further still, as the soundwave goes through space, it has greater and greater area to cover with the same energy. In the same way that the colour of a baloon gets less dark as you blow it up, the leading edge of the sound-wave gets softer.
As Drew said, it’s all about energy loss. It’s like firing an arrow. It keeps on going for a long time, but the drag from the air gradually slows it down over time, so eventually it’ll stop. It’s sort of the same with sound waves. If they hit leaves, walls, dogs and squirrels then the energy will be lost, until you’re far enough away that you can’t hear them.