Can anybody in the legal know explain why it is that more often than not a government official/politician in the process of being "discovered" for impropriety / corruption simply resigns and escapes the net?

Why is it that if Joe Public does something wrong he/she stands to be brought to book regardless of their whereabouts but a government official/politician can commit corruption and get off the hook by "resigning"?

The Terence Nombembe matter is a case in point and if one were to search back I'm certain there are many others.