That's an excellent question. In many places 'lobbying' is legal, technically it is supposedly to inform the clueless legislators about various interests. But in practice it very quickly turns into 'soft' corruption, meetings in holiday resorts (oh, do bring your family) and so on. Whatever lines are drawn the amount of money available to get around them is practically infinite and politicians (and civil servants) are not all equally good at determining when they are targeted and might be across the line before they realize it (and then it gets much harder to go back than to have never crossed it before).

Occasionally people are terminated, and occasionally there are prosecutions. But there is a very large amount of information about who may have been involved in corruption and only a limited amount of prosecution and investigatory power so the bulk of these cases will end up being ignored.