Well, GDP is a measure of how much your country produces. Why do things get produced? Because it can be sold. Who buys things? People with money. How do people get money? By working and being paid. So pay people more, then they'll buy more, then producers can produce more, then your GDP goes up. Is it that simple? No, of course not. But it's not a crazy chain of connections.
> How do people get money? By working and being paid. So pay people more, then they'll buy more, then producers can produce more, then your GDP goes up.
That sounds more like inflation than productivity actually going up.