Why there aren't any non-stop flights from SE Asia to north america while there are flights from australia/NZ to north america?

Not true at all.

There are a lot of direct flights from HKG, TPE, and MNL to both LAX and JFK.

Also, Singapore Airlines are scheduled to have direct flights to both LAX and JFK when A350 is delivered.

As for the direct flights from AU and NZ, the main reason is that

there is no reasonable connecting airports in between them and the north America while
you can connect from SE Asia very easily via HKG, NRT, ICN or TPE.

Why there aren't any non-stop flights from SE Asia to north america while there are flights from australia/NZ to north america?

為什麼雖然有澳洲/紐西蘭直達北美的飛機，但卻沒有東南亞到北美洲直達的飛機呢？

If your question are not for asking for translation, please neglect the above chinese translation.

也許是因為航權的原因? 如果飛機飛跨越國家時,它一定會涉及到主權和領土的問題
Perhaps because of freedoms of the air..? If the plane flies cross the country, it will be involved in the sovereignty and the territory.
有些國家是沒有給予其他國家擁有直達班機的權利
Some countries won't entitle other countries to have non-stop flights.