"Asians" are 60% of the world population and encompass a huge variety of cultures, as I'm sure many will point out. That said, it's viable to consider trends and averages, especially when scoped-down to Asian Americans specifically, despite the potential for generalization.
Two main reasons that are given:
Higher overall academic investment and achievement [1]. As per the study, Asians study about twice as much as white students and this shows in grades, SAT scores, and college admissions.
Second, a culture that places higher prestige on meritocratic and high-paying jobs. This is obviously a coarse-grained generalization of a very diverse set of cultures, but there's some truth to the stereotype that Asian kids have 3 career choices: doctor, engineer, lawyer. My impression is that this isn't disrespect for artistic and cultural jobs, but rather a realistic assessment of the chances of success in these fields. You want to get into art, fashion, photography, or journalism? It takes a lot of connections, luck, or both to land a good job in these fields. Doctor, lawyer, or engineer is a more reliable path to success.