Because it is the better choice for a variety of reasons.
Laminated glass skylights have three panes of glass which increases strength and improves the UV protection
Laminated units are generally required by local building code for overhead applications, especially for larger skylights
Laminated glass skylights are the only units that feature the new NEAT Glass
NEAT glass helps keep skylights spot-free with a special silicon dioxide coating that makes the glass surface extremely smooth causing water to sheet off the glass
NEAT glass helps keep skylights clean with a special titanium dioxide coating that interacts with sunlight causing organic matter to breakdown so it will wash off with rainwater.
Laminate glass is safer because of a clear membrane sandwiched between two panels of heat-treated glass, much like the windshield of your car
Laminated glass is up to 25% quieter than tempered glass skylights and 50% quieter that plastic skylights