Outlaw lobbying/lobbyists. What's next?
a) trade organizations (we're all the onion farmers in Nebraska and want to make sure the Nebraska legislature doesn't pass laws that negatively impact us and promote laws that help us)
and
b) activist organizations (we're a coalition of organizations that protect water usage in the Mississippi delta and want to pass laws that promote conservation in those states)
Those groups often choose to retain professional lobbyists but will also send groups of interested parties to lobby who are not professional lobbyists.
Do you also ban trade organizations and activist organizations in this case? Do you carve out exceptions for them and just ban the "freelance" lobbyists? Most lobbying is meeting with legislators and talking with them about issues, educating them. How do you ban that without making legislators effectively useless (or if you're cynical, even more useless)?
There is absolutely nothing wrong with lobbying, it is an essential part of the government and can not be legislated away, without crippling the entire country.
Just like, say, banning GMO bananas. But such regulation is a whole text which may need to define or refer to definitions of "GMO" and "banana", specify what's banned, exemptions, enforcement authority, penalties, and so on. Maybe 10 pages of legalese. It requires time, expertise, research. But it's still just a ban on GMO bananas.
Or a programmed UI button to show a message. Simple. The specifics of the execution are a separate matter.
It's not "indescribable", but no one will describe it to you ad hoc and expecting it is silly.