But you seem to be making the assumption that the processing of submission is somehow important, and that the editors have an obligation to the submitters.
Neither is necessarily true.
The editor who makes only one edit (not the processing of a submission, but an edit within the direcdtory) has accomplished something meaningful. They are not blocking anyone or keeping another editor out. Oh, sure, we'd love it if they did more, but they are not doing any harm by only doing the minimum, and to the extreme, if we had 10,000 editors who only did 4 edits a year, that is 40,000 edits.
You asked why an editor would only do the minium. The answer is almost always the same: real life. Editors reflect almost every possibly segment of world society. Editors in the military get deployed or transferred, parents have kids who enter or leave school. Some add to the world's population. People change or lose jobs, get bored or burned out, or decide to go on a sabattical. Rather than lose their editor account, they may do the minimum, or slightly more than the minimum so that when and if real life allows, they don't have to go through reinstatement.