[the88doctor]

A lot of the toasters shown from 1910-1940s only toast one side of the bread at a time and have a flipping mechanism to then toast the other side. The flipping mechanisms seem like they would be nearly as expensive as just adding a second heating element. So is the reason for the one-sided toasting a constraint on how much electrical power was commonly available to homes 100 years ago?

[detourdog]

The first toaster didn't come with a plug they came with a light-bulb socket connector.

If you are eating toast must be daylight for most people no need for the lightbulb.

Usually a home could afford a single outlet and they put it over the kitchen table for light and other utility tasks.

If one was going to splash out for some electricity that might consider and outlet for a refrigerator.