This isn't really about me as I am unlikely to sail a National OD event. But my reasons:
1. Purely budget. I am only 30 years old, single income and own a house in a ridiculously expensive market. An extra one or two thousand dollars will mean no bottom overhaul which is very much needed. I probably can't even afford the Dacron main.
2. Longevity (related to budget). If I race this main exclusively for 5 or 6 years, then I can retire it to cruising and maybe then buy a tech sail and have both. I have a lot of years of sailing ahead of me; no sense in going for broke right away and needing to replace an expensive sail and not having anything decent to cruise.
3. Winning isn't everything for me. I race with fun crew that one slow tack will burn up every inch of advantage a string sail gets me. Not worth the money to me. Besides, Dacron is still competitive in our PHRF fleet here and the rest of my sails are 1982.
I fully grasp the advantages of laminate sails to racing; I was actually "begging the question". Finished weights of the laminate sails is the easiest to manage as a OD rule but could never be deemed so heavy as to be a similar weight to Dacron, thus we fall back to the root of the issue: Dacron may not remain competitive against tech mains, so the class would need to decide if that creates greater costs for competitive boats.