plenty of possibilities here. One would be "The economic benefit was the most important for citizens, so most of them will probably try their best to reduce domestic waste."
Another would be "Citizens' first priority was to save money, so most of them will probably try their best to reduce domestic waste."
I suggested changing the wording in my examples to improve the flow of the sentence and to help the first part of the sentence transition a bit better into the idea of "so."
Hope that helps!
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