In March 2020, why did stock indices of Asian countries that curbed COVID19 still plummet? By March 1 2020, both HK and Japan restrained and quelled COVID19, compared to  France, USA, UK. Don't hesitate to discuss other countries unscathed by COVID-19.
I cite some of  better comments from r/investing and r/stocks.

Because all their customers are in countries that didn't curb it.

Everyone else follows America. US equities are half the value of all equities in the world.

I would guess that Asia is an export economy largely to the rest of the world so tends to correlate with the rest of the worlds performance. However, the P/E ratios are likely lower than what you'd find in the developed world so there might be some opportunity for good gains when the broader economy picks up.

Because there was a gigantic flight to the US dollar in March. Pretty much every single asset across the board (yes, including safe havens like gold and US treasuries) fell versus the USD.