I will not speak about the supreme talent or the sexy looks, in case of Tusshar Kapoor it was the bad choice of films & in case of Uday Chopra, it was over-confidence. Otherwise, Tusshar is still the one who had a hit debut film & also winning best debutante filmfare award. After that he chose either Telugu remakes since his Mujhe Kuch Kehna Hai itself was a Telugu remake, all of which bombed at the box office & all these movies showed his drawbacks as an actor.
In case of Uday Chopra, well like his other co-stars in Mohabbatein even he couldn't make it big. Sure, Mere Yaar Ki Shaadi Hai was there but it was evident that he wanted to play the central character in the movies which were of Srk's trademark, that's why he was seen in a special appearance in Mujhse Dosti Karoge. And also the bad luck, his Charas was directed by Tigmanshu Dhulia & if such a director can't help him as an actor then nothing much is left to explain.