ALOT of Asians who end up doing Chemistry and Physics in Senior Years have most likely been influenced by the high scaling around the subs, the 'delusional' need to do them, fitting in with other Asians, think that they actually 'like' the chem and phys (I think if you genuinely like those subs then you don't even need to go tutor unless you're lazy [okay, I'm hypocritical about this but my point still stands]), they know it's the standard subjects for Asians and Asian parents tend to loves the sciences and maths as opposed to the humanities (Economics is really the only exception to this).
Another big reason are siblings and relatives, Asian parents love to compare to relatives and others so they'll say something like 'Yeah, your cousin/brother/sister got 99 ATAR and she/he did 4 Unit Maths, Economics, Chemistry, Physics and Advanced English so you must do these subs as well'.
Also, heaps of Asians go tutoring and tuition centres emphasis the need of high scaling subjects such as 4U Maths, Chemistry and Physics.
This could be generalisation but I think some of what I said are true to an extent... I'd know of course cause' I'm Asian too ><