I have it!
We have a built in time of turmoil, in the War of the Ring.
There had been two eorls, the East Emnet and the West Emnet, with Meduseld as a "final arbiter". It was, however, most convenient for the people near Edoras, such as those of the Middle Emnet, to use Meduseld as their
first court.
But the War created problems. For one, Saruman was keeping Theodred and Eomer (the two eorls) too busy, and (here's where things come in for the Middle Emnet), orcs and Dunlendings were running about. Now, granted, neither orcs nor Dunlendings had gotten to what is now the Middle Emnet, but
Wormtongue had Theoden in thrall, for who knows how many years?
Now, while the three lords who are the war heroes in the area were away fighting, you had scum such as the previous owner of Scarburg taking advantage of Theoden's illness, robbing and pillaging as he pleased, and that didn't stop with the end of the war - now Theoden is dead and Eomer is very busy trying to reestablish order, doesn't have time for the regions near Edoras, so he appoints Eodwine as Eorl of the new Middle Emnet.
But before he does that, the three ware heroes are back, and use the nefariousness of what's-his-name who was at Scarburg, as their excuse to establish themselves as local arbiters, creating an expectation and precedent for themselves to be - sort of - sub-eorls. So there it is, and they got used to it, and they didn't take kindly to there suddenly being a new Eorl in the area who has the king's authority.
So the simple non-warrior landowners - farmers who are not warriors - are by this time poor, their lands overrun, depleted and whatnot by robbers and such, and the three lords taken advantage of their suffering by putting them in their debt - easy enough to do by loaning them what they need at sharp interest.
What do you think?