As another already stated, I don't think the issue is so much lack of need for knights, but lack of available knights. Most any size estate you can create in a rural is almost never going to be as lucrative as a good sized city or town estate; very true and felt in smaller realms.
I do see plenty incentives for lords to still want knights though. Political power( given referendum styles), military leverage in armies, stewards, being more efficient at civil work, and the benefits of them looting foreign food, to name a few.
The difference in gold production is intentional and realistic. The only perks I could maybe see as a viable incentive to WANT to pay more to knights would be to make civil work more powerful in certain region types- which to me is pointless on a normal situation other than raising the sustainable tax rate.
Or, wait for the long ago discussed buildings for estates that offered much potential. This potentially new feature is as cool as the new estate system itself, but likely to get next to no fussing other than bugs and people wishing for more buildings.