Should not lobbying be... illegal?
As a kinda-sorta-lobbyist (not a registered lobbyist, though I do occasionally log hours) I'm probably not the best person to respond to this, but originally/hypothetically/ideally the point of lobbying was/is more or less representational petitioning.
For example, say there are a group of workers in Chicago who want better rights for workers, but a) don't have the time to formally petition the government / visit the halls of congress, and/or b) may not know the details of exactly how/what, even if they know the broad strokes. In theory, a lobbyist would represent those people. They'd know how to turn ideas into legislative/regulatory proposals, how to communicate with members of congress, and how to best try and get those policies into effect.
In theory there would ultimately be lobbyists representing all the various interests out there to make sure that members of congress are hearing from everybody. In practice there's obviously a power and resource imbalance between various interests.
Just banning lobbying would likely mean that those with the most 'natural' presence in DC - or just those with the best personal relationships to members of congress - would have the most access and power. It's a hard thing to regulate/limit.
Edit: And yeah, there have been many attempts over time to limit the corruption involved. Per the comment below me, I think there was only a relatively brief window in all of U.S. history where the lobbying and corruption laws were actually pretty decent nationally, but they're definitely in a bad place these days. Certain Supreme Court decisions over the past ~15 years haven't helped with that, either.