I think there are both practical and personal reasons. The practical reason is that Harry Potter is indeed a rather special production, and its impact is not only on every Harry Potter fan who watches it, but also on every actor involved in the show. Harry Potter was phenomenal, with eight installments made in one ****, and every single one of them was beloved by everyone. The entire eight Harry Potter films are basically y rooted in every character in them for every fan who loves it, not to mention a few of the main actors in the production.

And Master Malfoy is the main supporting character besides the three main actors, and has a very large role. Every single one of the kids in Harry Potter made a huge impression because of this very good production. They got big because of it, but they also have to bear the negative effect of this honor, which is that they have already left a fixed impression on everyone, and it is very difficult to transform.

It's just like China's Family Guy. Several consecutive serialized family dramas brought the likes of Yang Zi and Zhang Yishan not only great fame, but also the fixed impression that everyone gave them. In the many years to come, if they want to get out of this situation, they need to come up with a better state and stronger strength, presenting better works, in order to let everyone see a different them.

And then there's the idea of Tom Felton himself, I guess. It is said that after the end of Harry Potter everyone else was crying with excitement, only he was happy is to be free. Maybe freedom was more important to him than making it big, it's really very true. Supposedly later on he became a singer and did some work, but none of it was as impressive as in Harry Potter. I think that's mainly probably why.