Exactly.

There's so much stuff like that going on it's hard to know where to begin with these people.

For example, demographics. If you have a large young population and a large elderly population you will have a median income pushed lower than when your demographics skew middle aged.

Also, when you have large immigration influx, that forces down your median income as a percentage for the whole population, even if the people who were there before the influx are doing considerably better in real dollar terms.

Or if retirees are doing part-time "fun" work for small amounts of pay, when they wouldn't have been 50 years ago, that'll force down median income since they're not competing for higher wages.

It goes on and on.

In this case, the increased labour participation should create some supply of its own.

You keep missing the point. Women traditionally worked low paying jobs, like housekeeper or nanny. The increased participation of women in the workforce mean that women now work higher paying jobs. It does not mean that that someone has gotten more real pay for the same job. The numbers you linked to on worked hours still hasn't had meaningful change since the '80s. If your point is that things got better until the '70s or '80s but not since, well then I agree with your point. But like I said there are of course many factors, like men are probably working less hours, but on the other hand underemployment has gone up.