This is a good point. It seems that only cooking is mandatory in any of the communities. The job of the treasurer is also relentless.
Landscaping is relentless.
For us, cleaning the commonhouse is relentless. I'm assuming that several people would be cooking, not just one. Some would like to cook more often than once every 10 weeks, and others wouldn't. Some want to do the job of purchasing, negotiating with local farmers, etc. The answer of why cooking is mandatory seems still to be unanswered.