Various reasons, see: https://en.wikipedia.org/wiki/Electricity_on_Shabbat https://en.wikipedia.org/wiki/Electricity_on_Shabbat and https://en.wikipedia.org/wik

Various reasons, see: https://en.wikipedia.org/wiki/Electricity_on_Shabbat https://en.wikipedia.org/wiki/Electricity_on_Shabbat and https://en.wikipedia.org/wiki/Activities_prohibited_on_Shabbat https://en.wikipedia.org/wiki/Activities_prohibited_on_Shabb... It's important to note that not every member of a religious group interprets rules or follows them in the same manner. There are strict Orthodox Jewish sects that hew closely to these laws, and I've known many people from a Reform Jewish background who don't even keep Kosher. You see the same thing in Christianity with branches having varying degrees of liberal/strict rules. Individuals within those groups are even more varied still--for example many Catholics visit the Church only for Christmas/Easter and use birth control.