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Truefact. Most times they cast lesser than 100% just as you have said.
Your influence on the platform matters alot and determine what you can do and undo

They may also be “apathetic” if they like Steemit, but not enough to vote 10 times a day. Another possibility, is that they do not wish to manually find ten posts they find worthy of voting on because of the time necessary to do so. In both of these cases however they should certainly STFU about unfairness.