I get your point. not only that businesses might be taken over by other gangs for example. In phoenix there could only be like 5 gang owned restaurants. Of course, gangs could start it but it doesn't necessarily mean other gangs can't take over your business.
If it costs as much as the houses etc. Then another gang taking it over will be a bitch. I mean buy a business for like 10 mill, only to have it taken by gangs?