This is purposely done when the commercial is made. Internet advertisers are starting to do it too.
The reason we get “blasted” at commercial time is determined by how the audio levels are recorded when creating their ads. Affectively, the process is called dynamic range compression, or “compression” for short. Compression is applied to reduce sounds that get recorded over certain levels while the quieter sounds do not get reduced. In the process, the advertisers take liberal advantage of the mid range tones to exploit our senses, since those aren’t affected as much.
To sum it up, compression is used to increase the average level of sound, effectively making it louder.