How isn't it?
What do you think lobbying is?
I go to a politician and tell them that I want such and such a policy. If they don't vote my way, I won't vote for them the next time they run.
Maybe that's not lobbying in your mind. Perhaps you only want paid lobbying. So I own some stock. Those companies can pay lobbyists. Those lobbyists then contact politicians to advocate for policies that favor that company. How do they do that? By talking to the politicians. And if talking is not free speech, then what is?
Perhaps it's the payment that is problematic. So let's assume that we ban paid lobbying. I am paid by my employer. If I advocate for a position on my free time, am I breaking the law? It seems obviously no if I'm lobbying for something unrelated to my employer. But what if I work for Tesla and am advocating for subsidies for electric cars?
If my official title is website developer, is it all right for me to lobby the government? When does it become illegal then? What if we hire Paul Manafort as a website developer? Can he then lobby?
How about a CEO? Or a director of marketing?
What if I work for another company that does work for Tesla? Can I be director of marketing for another company and advocate for Tesla?
Either you are preventing me from sharing my opinion with the government, even though I'm not what any reasonable person would consider a lobbyist. Or you are allowing Paul Manafort to lobby, as a "website developer" working for a contractor providing services to a company.
How is this not a free speech issue?
Maybe you would be happy with some really complicated set of rules that bans Paul Manafort but not me. But it's still going to be a free speech issue in the same way that yelling fire in a crowded theater is a free speech issue. It may not win as free speech. But it will still be criticized on the basis of violating it.