Why are circuits in home connected in parallel?

Answer 1

You want every electrical device in the house to have equal access to the 117 volt utility supply at the
wall outlets. That means that every device in the house must be connected directly to the pair of wires
entering the house from the pole ... which is a pretty good definition of a "parallel" configuration.

Another reason, purely pragmatic, for not wiring household devices in series: Just like the old-fashioned
technique for constructing strings of Christmas-tree lights ... if household devices were connected in series,
then every device in the house would have to be switched ON, otherwise none of them would work !
If any single device were switched off, then there would be no current path through the series string.

And here's another little thing to consider: In a series string, each individual resistance in the string
has an influence on the current through the string. As a practical matter, that means that if everything
in the house were connected in series, then as the toaster heated up and its resistance increased, all the
lights in the house would dim, and the refrigerator would run a little slower. Definitely inconvenient.