I dont know why Ford didn't put it in 10lb flywheels, probably for the same reasons they didn't put in Cold Air Intakes, K&N Filters, LSDs, Superchargers or all the other goodies that you can buy from performance shops.
Or maybe because someone will always comeup with something newer and better "its called progress" coming up with innovative and more advanced parts.

95 SE MTX Midnight Red
Dual Extrude Honed SVT Intake Manifold / 65mm TB / SC Cold Air Induction / Ford Racing 9mm Plug Wires / Quaife Limited Slip Differential / Centerforce Dual Friction Clutch / Fidanza Flywheel / UR Underdrive Pulley / Custom Dual Straight Flow Exhaust / StreetGlow Sport Pedals / Tint / Pioneer Deck and CD Changer / 2 12" Orion XTR subs / 2 MTX amps(425&280watts) / Phoenix Gold Titanium Bass Cube and Wiring / Boston Acoustic 5x7's, and Rockford Fosgate Tweeters. Next: 19# injectors and chip
Rebuilt engine @180,000 km
Rebuilt tranny @215,000 km