They're not. Lobbyists are breaking federal law if they take a congressman out to a nice dinner.

Paying them more wouldn't solve this problem because running an election campaign is so expensive that they spend the majority of their time trying to raise money. They end up taking positions that are friendly to potential donors in the hope that the donors will keep sending them money.

The major problem isn't that they trade favors to lobbyists to enrich themselves directly (although some undoubtedly are), the problem is that they trade favors to lobbyists in order to keep getting re-elected.