America has no such restrictions. Members of Congress & the President start running & fundraising now ~2 years before an election (& unofficially before that). For the House of Representatives, that means members are in an electioneering & fundraising mode non-stop. The staggered election cycle in the Senate means that a large portion of the Senate is constantly campaigning further making focusing on the act of governing difficult. Fixing these issues doesn't solve all problems obviously but making no reforms isn't going to improve things either.
Not the OP, but ... murder or genocide is very clearly a crime, while lobbying starts with "talking to an elected official about laws that concern you", which is sorta normal in democracy, the elected officials should be available to talk. It only becomes problematic if it is overdone or done too secretively.
I think that a good and transparent lobby register is probably more useful than outright ban; at least an external observer can glean some information from it.
For the purposes of discussing government corruption, "lobbying" mean "talking to an elected official about laws that concern you, with the implication that their response will affect how much and in what direction you use money to pervert the electoral process". (Obviously, corporations generally don't actually explicitly say that part, because plausible deniablity.)
Lobbying is already legal, and is mostly a bad action; but if we make it illegal, it will create a black market that isn't regulated. It's the same problem (one of many) that the "War on Drugs" had, in that any activity that's illegal tends to be unregulatable. It also attracts to the market for people who are already doing illegal things.
I think the root of the problem is that politics in the US (and in most other places) is a popularity contest; it attracts people who are charming, lie effectively, and who's goal is to be popular. They, of course, have other goals too, but having the accolades of the represented is a requirement, and people that seek that status end up drawn towards politics.