Adults and collectors can pay more and "nerdy" or "childlike" subcultures are viewed as mainstream.
Both of these are symptoms of the fact that societies are growing older - the median age of the US was 35 in 2000 and is around 40 in 2025. Similarly in the EU the median age was around 38 in 2000 and is around 44-45 in 2025.
Additionally, tastes change and childhoods change. For the younger generation, Minecraft and Roblox is their Legos, and for the generation before the "Lego" generation it was Erector and Mecano sets.
The norms and tastes of a boomer who grew up in the 1970s or 1980s is somewhat out of touch with younger generations, just like how someone who grew up in the 1920s or 30s was out of touch with someone growing up int he 1970s or 80s.
In 2026, the 1980s is as far back in history as WW2 was in the 1980s. Legos weren't a defining part of most childhoods globally, and there's no reason to assume they still would be.
Younger generations will wax nostalgically about Minecraft or Roblox in 20-40 years as well.