You got me wrong...
... and got me wrong pictures in my head.
First: Dirt it self hasn't changed. But the soiling of clothing has. My father still wears his work socks, shirts etc. at least 3 days. I wear my shirts one day. While 30 years ago a bigger percentage in the EU and the US worked in "dirty" jobs (farming etc.) with those different soils, that amount reduced until today. So the average soiling has indeed changed by today.
Self-cleaning suds: Whirlpool displayed it so nicely. As your wash water sits in the tub being saved, heavy soil particles settle to the bottom, lighter soils float on top of the suds. As the suds are returned, those lighter soils as well as the heavier once stayed in the tub. The wash water cleaned it self to a certain degree.
With todays soiling, that process is less effective.
But on the other hand, todays laundry is generally less heavy soiled and thus suds might be reusable still.
Laborintensity: So, just to get it right: You plug your laundry tub, place the drain hose into it, start the first cycle. The washer washes, drains and then spins, draining into your saveing area aka laundry tub. The rinse starts.
Now, you want to drain the rinse water away and not into your saved suds. So, while that 5-10 minute window, you'd have to be at your washer in time to move the drain hose out of the tub so the water drains away. After another 5-10 minutes, your laundry would be done. You'd move it to the dryer, fill the washer with the next load. Now you'd place the hose back into your saved suds and let them be pumped back in. You'd unplug the tub as you don't want to save the suds again and let the washer finish it's cycle.
So, you'd need one additional visit to your washer that has to happen in a 10 minute window. You'd have to move the drainhose 3 times within that procedure. For me, that looks like work. Not much, but enough to cause inconvenence. Especially if laundry us situated in areas where a laundry tub might be more common to find like a basement or a garage.