Why isn't Mattel trying to make a shared universe like Hasbro?

They could if they wanted too. Mattel owns all of these.

American Girl
Apples to Apples
Barbie
Big Jim
Computer Warriors
Dino-Riders
Enchantimals
Ever After High
Extreme Dinosaurs
Food Fighters
Hot Wheels
Imaginext
Jayce and the Wheeled Warriors
Kid Acero
Magic 8-Ball
Masters of the Universe (He-Man)
Matchbox
Max Steel
Mega Bloks
Mighty Max
Monster High
Planet Heroes
Polly Pocket
Rescue Heroes
Rock 'Em Sock 'Em Robots
Street Sharks
The Incredible Crash Dummies
Uno
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Xtractaurs