He isnt famous outside Juve/Calcio fans for some reason.
People of a certain age would say differently, but I agree that he has become forgotten a little over time by people who don't follow football as strictly.
I've worked with several people over the years who were 50 or so years old who watched Juve live playing against their teams in Europe (Villa, Liverpool, United, etc.) and when I ask them about the games they always say what a hell of a team Juve were, with Platini and Boniek in particular, the toughness of Gentile, but they always mention Scirea, just an unbelievable defender and footballer, could do everything, and always with precision.
He has fallen into the shadow of Beckenbauer and Baresi in a similar kind of role, and I think a lot of it is because of multiple successes over a period of time. Scirea won the World Cup and the European Cup, ICC, many trophies, and he was extremely likeable, but he doesn't have multiple tournament success, didn't play in such a dominant international or club team. You can tie this argument in with that I said in the other thread (De Ligt?) about Juve not taking their chances to win multiple tournaments when we had a great team (80s and 90s).