1) HFT is more than just US equities. Many exchanges are open 23 hours a day.

2) Many HFT firms do not specialize in 'news-reading'. That is, they will sit out periods when an expected announcement is coming. You can observe this by looking at the liquidity of a product just prior to an expected relevant news release - there will be very few orders.

3) There are more events than just news events that require speed.

Sure - market-makers need to react quickly. But that's only during the hours when the market is open. If there's no market, no-one needs to be quick about it.