Lobbying hasn't been declared illegal because the very ones who participate in it are the ones making the laws an upholding the laws. It is a full circle of corruption in a legal way. It has been done through the years for so long, it is not only legal but acceptable and expected.
Lobbying is actually just legal bribery but since both parties get what they want, one gets money and the other gets their way, it continues and probably always will. There have been some attempts to stomp it out but those attempts were interceeded by none other than the lawmakers themselves.
So, what has been will be. There is really no way to make all governments just and upright. They never have been and never will be. Money and power will always rule over people and those who don't realize that are the decieved.