I've been in quite a few jobs where the work floor is rather large with a lot of people, and the sound system is terrible. Some parts of the floor you can hear the system just fine, while on other parts you can't really hear it all.
How hard can it be to get a good, even sound over an entire work area?
Sound design is more complicated than you might think. If you just throw up some speakers without paying attention to directionality and wattage as well as room characteristics, your system will not sound good.
I've noticed this as well. Some restaurants and stores I have gone into the sound has been terrible. There are spots where the music is too loud and other spots where the music is not loud enough. I think if you are going to put up a sound system, at least make sure it sounds right first.
If I can take a guess it's largely related to funding. Places which are not audio-oriented will just buy small, simple speakers and put the radio on. I suppose audio for big space will need proper amplification and speaker placement, which are usually neglected for big spaces.