>including after office.

A politician might cover or be involved with a lot of different industries during tenure in office. You can't go to work in any of them after? What if you're one-term-and-done at age 45? What are you supposed to do?

Sure, you could ban them. That's a sure-fire way to a government of low-competence, career politicians.

Depending on the state, lobbyists generally have to be licensed/registered and report all their contacts [0]. I have a family member who's a registered lobbyist: as a lawyer for a regulatory agency, she sometimes represents its interests in dealing with the legislature that authorizes it.

[0] https://www.ncsl.org/research/ethics/50-state-chart-lobbyist...