Without electricity, how would the furnace communicate with the thermostat, and how would the blower fan motor operate? Convection goes up, but not necessarily out, and without a blower fan there's risk of the furnace overheating.
To me, radiators are the best heating system, too bad they have been out of favor for decades.
But I think it's pretty easy to understand why it's unpopular. First, AC is popular in the US, so a system that can reuse the same ducts is a lot less expensive than something entirely separate. Secondly, it's a lot simpler and cheaper to service. If your hydronic heating system freezes or develops an airlock or springs a leak, you might be looking at five-figure repair costs.
In the old furnace, every so often you would have to add water, depending on how cold it is outside.
The house was build over 110 years ago, so electricity was not too common back then. I probably think the source of heat back then was a coal furnace.
I'm curious, why? I've never lived somewhere with radiators, so I perhaps don't know what I'm missing.