Because 28oz is more ideal than 50oz. I was going to go 50oz, but I changed my mind and told my builder to go 28oz. The less weight hanging off the ends of the crank the better. I'd have gone 0 (neutral) but my crank can't do that. probably doesn't make a huge difference but I am buying a new flywheel anyway so I went 28oz.
d&d performance sells a billet steel flywheel for $199 with dowel pins. You can use this flywheel for 0, 28 or 50 oz by using the right weight. This is what i'll be buying in a few weeks.