why only 3 nominations per person, & only 3 requests for people who sign up

There wasn't really one reason we settled on three, but at the early stage of our planning, we decided on three for across the boards in terms of nominations/requests/offers due to administrative reasons, e.g. it would simplify matters, be less numbers to keep track of, not make the list of fandoms too unwieldy to manage, etc. I hope that answers your question? And thank you for your support!