Very often, it's probably due to a lack of knowledge, a poor understanding of the regime. Some people tell me they didn't think they were lobbying. Public servants are the ones who tell them that they should think about registering because what they are doing is actually lobbying.
That said, it tends to be the same people who are always late. Maybe it's about money. They engage in lobbying without registering, and when it winds up in the news, they decide to register.
It might be a good thing to be able to impose a penalty after a small investigation, instead of referring the matter to the RCMP.