That's surprising to me. I think I'd really enjoy being able to send food and/or production around.
In particular, I'd love to be able to build a little village in a location where lots of food was available but was otherwise not very interesting/useful; farm the area, and then send food to the capital at the rivermouth nearby. If city maintenance cost was largely determined by population (and possibly the buildings in them) rather than city count, we could end up with a much more realistic situation where you have just a few large cities (with lots of buildings in them), and many more small towns scattered through your empire. The towns just gather nearby resources and have only the basic services (buildings). You should be able to build little towns without fear of collapsing your economy, and should not expect all settlements to become enormous powerhouses as is the case now.
I can see it now, my lovely empire... Lots of farming villages in the plains around the lake and over near the sea where the grass is green. A major industrial city lies where the river leaves the hills; this city is most productive because it contains several Factory buildings, which provide specialist slots for Workers, who provide production in the form of "Shields" (which are no longer principally sourced from working mines). This industrial city is currently the only city in my empire with the expensive Tank Factory, allowing it to build tanks. It imports lots of food from the nearby farms to feed the factory workers. Further down the river, at the sea, is my capital, which has Universities, Libraries, music and culture, religious temples, trade buildings, and all the grand administrative buildings which the capital of a major Empire should have. Up in a mountain valley, an old mining town has been slowly growing, and has just built a steel mill, to refine the ore it mines nearby. It'll probably develop further industry of its own, eventually. On an island offshore, I've built a thriving fishing industry (buildings which increase food such as the fishermans' huts); this town also sends food home to the capital. Recently a village was founded in a valley leading to a strategically important mountain pass: a rival civilisation might be tempted to send an army through that pass, so this new town is being developed with defensive structures and military support infrastructure such as a military airfield.
Too hard? I think it'd be awesome!