I see this question asked many times around the Internet in different places or some derivative there of.
First off what people need to understand is that companies rarely update their computer systems as fast as you would at home. A large company roll-out takes at least a year from start to finish, not to mention that is a large chunk of change to spend. If you are missing the resources to complete either of these tasks, your upgrade may happen pieces at a time or not until the resources are allocated.
Another reason is application compatibility, this goes hand in hand with the above statement. If you don't have the resources to test manage the new systems what good would they do your company?
What does this have to do with AV software you ask?
The above examples leads to "legacy" systems being ever present in a corporate environment, since legacy systems are much less powerful than what you would use on a normal day at home the AV industry has taken note and tries to keep the resource usage down.
Speaking of resource usage, this is kept down in most corporate antivirus' by "dialing down" the protection at the end user level.
You may think that is a little crazy but what needs to be kept in mind is that in a corporation there is much more supporting hardware in the network to alleviate threats at the entry points rather than at the end user level. Thus negating the need for "useless bloat" in the program.
The last major reason in my opinion is user intervention, in a corporate environment work stations are managed by the respective IT departments and require little, or more often no user intervention. In complete contrast home users are expected to be able to manage their own systems and more than often they fail miserably in this respect. Just have a look at the root cause of botnet effectiveness. Antivirus vendors realized this early on and are trying to automate and more clearly explain the needs and actions of their software solutions, thus increasing "heaviness" of the utilities.
So in conclusion to the main question of "Why are corporate antivirus solutions lighter than home versions" there is not an almighty above all reason, but in general it is due to user intervention, needs, and money.
I hope this post shed some light on the situation, and please note this is not a definitive answer but rather a general observation.