Because there is no easy way to ban in a democracy. Originally, the term means someone who hangs around in the lobby of congress (or such like) and talks to representatives when they come through. Imagine this is just some ordinary voter who has an important issue on their minds; perhaps someone like Raphael Lemkin. He did that. Non-profit organizations - like Greenpeace - lobby, as well. It's hard forbidding lobbying without unintended side effects.

Even if you did, it might not get you where you want. Representatives would still have an open ear for major employers in their districts. After all, voters want those jobs. Representatives meet those bosses on many occasions, like charity events. Money and power can be used to get more money and power.

Personal access is only a part of it, anyway. People influence the media and fund political ads. There's also funding for think tanks and universities. People with money and power (or fame) can do more of that.

Don't assume this something that just happens behind closed doors out of the public eye. For example, you may have noticed the recent kerfuffle between actress Scarlet Johansson and OpenAI. OAI allegedly hired a voice actress that sounded too similar to ScarJo. This community here seems to have largely sided with ScarJo. Which means that they want famous people to receive a rent for lending out their voices; a rent which will be ultimately paid by consumers. And if you have a similar voice? Tough.

This is exactly something that many of these AI lobbyists are paid to achieve. They are supposed to get money for the rich people who pay them; preferably without the rich people having to do work.

How are politicians supposed to learn about niche issues in the private sector?