There is multiple research trying to figure out which one is more motivating at work.
For me, the most interesting finding was that both of them can be the main reasons, but they influence each other. That means if the cause is the main reason, even if they get less money than in a normal position, it still captures attention about the cause, so it's better if it operates on a voluntary basis. However, if people only do the job for money, then salary increases and bonuses bring significant changes to work morale.
Personally, the cause has always been more motivational for me. Knowing that what I'm working for makes a positive impact. How about you? ☺️