Why someone who is popular as a child actor is not famous as an adult?

There are a lot of celebrities whose childhood versions we've seen on film when we were probably too little to remember, but now that we're older, we recognize them in adult roles! Darsheel Safary, who played Ishaan Awasthi in Taare Zameen Par, has remained imprinted in our minds long after the film's release. He is now seen in short teen web series. Sana Saeed, who started as a Bollywood child actress starred in the much-loved rom-com Kuch Kuch Hota Hai has reached adulthood! You've probably seen her in Student of the Year as well. Malvika Raaj is presently performing in Telugu films after her performance as Kareena Kapoor's younger self, Poo. Before I forget, I'm sure you all remember Munni from Bajrangi Bhaijaan. Her real name is Harshali Malhotra, and she's all grown up and quite active on Instagram, where she posts her dance videos. But now that I see them, I feel like they were more popular when I was a kid than they are now, which is kind of depressing. What do you think the cause for their lack of popularity was when they were adored by so many people?