It also hurts NBA cause too many undeveloped players getting time over vets. Teams play the young guys because they have potential and need the playing time to develop it, but it degrades the quality of play. As opposed to back in the day when they got that development in college so rookies could come in and be all-stars from Day 1.
Rookie all-stars by decade:
1950s: 11
1960s: 11
1970s: 6
1980s: 10
early 1990s: 4
late 1990s: 1
2000s: 1
2010s: 1
I split up "early 1990s" and "late 1990s" because the rule allowing high school drafts came in 1995.
Before then, being an all-star as a rookie wasn't common but it wasn't unusual either. Hakeem and Jordan in '85, Ewing in '86, Robinson in '90, Mutombo in '92, Shaq in '93, Grant Hill in '95.
Afterwards? It was almost unheard of, and it has ONLY been the older players who made it. The only three rookies to make the all-star team since 1995 were Tim Duncan (22yo), Yao Ming (23yo), and Blake Griffin (22yo). Three rookie all-stars in 28 years after having had 14 rookie All-Stars in the previous 15 years.