Your observations are indeed correct except that the unwanted (and un-named) phenomenon is not as a result of a lack of humus (which on a separate note does not exist except in a laboratory, but that is another story lol) but the direct result of Tilling the soil and the destruction of soil integrity that within days of tilling destroys the established microbial biome in the soil and thereby the integrated soil structure.
You can add as much organic material to a soil as you like but any benefits it will add is all wasted by the mechanical tilling of garden (and field) soil.
In some remarkable coincidence, this afternoon, I was watching an excellent video from 2011 which compared soil that has been tilled continuously and soil that has not been tilled (No-Dig as we say in the UK) and the agitation and breaking of light bonds in a soil that is tilled results in a separation of all the components and the demise of the rhizosphere micro-organisms.
Until today, I did not quite appreciate how our little bacterial and fungal friends create an active web of soil pores and pockets using exuded poly-saccharides that hold the soil together, binding all the components, organics, sand, grit, clay into one consistent component that gives a sustaining structure that permits both better drainage and aeration as well as better uptake of fertilisers.
It also explains why, to me, someone who concentrates on container gardening, indoors and out, why it is so important to create a well-balanced aggregate and organic mix that provides a stable 'home' for the unseen heroes of the Soil Food Web.
In just 2 simple and short field experiments the presenter, USDA-NRCS Ohio state agronomist Mark Scarpitti perhaps answered all 4 of your observations for what you refer to as Tilth (defined as tilled soil) compared to non-tilled/No-Dig soil.
In Experiment 1 where they ran water over 1 of each soil, the tilled soil collapsed into its individual components according to particle mass. The No-Dig soil retained its structure after being soaked in water.
In Experiment 2, he put 'rainulators' on blocks of the 2 samples. In the no tilled sample there was no run off of water (and phosphate) and complete absorption of water. In the tilled sample the lower mass particles effectively closed off the soil surface and almost all the water (and phosphate) ran off - so no benefit to the tilled soil.
I hope you have the explanation to your 4 points and can as a bonus appreciate that you perhaps should be adopting an No Till/No-Dig methodology in your garden.
For more info on No-Dig (which also saves a lot of back pain) the UK exponent of this method is a lovely man called Charles Dowding and he has written some good books on the subject and some enormously interesting videos on YouTube. I must point out that I am not in any way connected to Charles except having watched his videos and bought one of his books (at full price) on his No-Dig methods which are, I think extensions from the earlier methods of Ruth Stout from the 1930s USA.
So here is the link to the short video from Mr Scarpitti
Tilled v No Tilled Soil
So perhaps we could call the phenomenon "Why we shouldn't till our soil" .
I jest of course but the effects are frightening insofar as water run off from tilled agricultural land adds to soil erosion, raised river levels and the pollution of waterways due to unbound nutrients such as phosphates. It also forces growers to add greater levels of fertiliser to combat reducing yields. And I dare say other bad events.
No-Dig/No Till will not overcome these things in one season but over even a short time, its positive effects will make your observations a thing of the past, whilst helping all gardeners and farmers to improve their yields for almost zero cost.
