It’s basically a control technique. Starts with brainwashing at an early age, being brainwashed yourself, and then capturing ‘goodwill’ of similarly brainwashed people, to push agendas over others, that in the end result in either money, respect, or fear - all 3 over other brainwashed people. In some cases its done by people who aren’t actually religious, in other cases it’s brainwashed people who believe they are a hero for the cause or need a sense of belonging badly and are surrounded by other brainwashed people. If its political then they have electoral reasons to justify it. Some people follow the herd mentality and put of desperation fall to religion thinking their issues in life would be solved by ‘praying’ to a larger being. Once in, they believe they need to follow the ‘rules’ to be rewarded in life, failing which atleast they’ll be rewarded after dying. The idea of a continued life after death also appeals to them as some form of eternal living, with again a punishment system in place if they do not live by the rules as laid down by the ‘superior’ beings who took down notes from the highest authority who decides if you have a chill time after dying or burn forever.

All in all, I feel its one or more or all of these - power, money, fear and self-righteousness - as the justification they have.