Why don't people always use lossless audio formats?

Even though lossless audio is a perfect copy of the original, a file created with lossless compression will not be as small as a file created with lossy compression.

So if you have a limited amount of data storage on, for example, your portable music player, smaller files will mean you can fit more files on your player storage.

That is, using lossy compression may reduce the quality of the music slightly, but it allows you to take a greater number of music tracks (or albums) on the bus to work.