Wages have not been stagnant across all sectors of the economy. Certainly some jobs aren't valued as much, and their value hasn't been growing or even keeping pace, but there are plenty of areas where wages have been increasing quite a lot over the last couple decades. Given that this is generally a tech-focused forum, that shouldn't be news to anyone here ;)
How would you explain the stagnant wages of the last 4+ decades compared to the massive economic growth? I don't think there's much evidence that the relationship between labor supply and economic growth is anywhere near one-to-one (e.g. one more person working means their wage is added to the volume of labor demand).