Why has Thailand closed its borders and ports with Malaysia?

I don't see any exception for Thais in the earlier closure:

MALAYSIA - published 18.03.2020

1. Passengers are not allowed to enter Malaysia.

- This does not apply to nationals of Malaysia.

- This does not apply to permanent residents of Malaysia.

- This does not apply to passengers with a diplomatic passport.

2.Nationals and residents of Malaysia are required to be self-quarantined for 14 days.

3. Nationals of China (People's Rep.) with a passport issued in Hubei, Zhejiang or Jiangsu Province (China People's Rep.) are not allowed to enter Malaysia.

- This does not apply to passengers who reside in Malaysia.

4. Passengers who have been in the Hubei, Zhejiang or Jiangsu Provinces (China People's Rep.) in the past 14 days are not allowed to enter Malaysia.

- This does not apply to nationals of Malaysia and passengers who reside in Malaysia.

5. Passengers who have been in Hokkaido in Japan in the past 14 days are not allowed to transit and enter Malaysia. - This does not apply to nationals of Malaysia.

- This does not apply to Malaysian permanent residents, Malaysian social pass holders and Malaysian student passes holders.

6. Malaysian Permanent Residents and Pass Holders (Long Term Social Visit Pass and Student Pass) who have been to Iran, Italy or Korea (Rep.) in the last 14 days must undergo health screening by the Ministry of Health (KKM).

7. Operating Airline Crew who are nationals of China (People's Rep.), Iran, Italy and Korea (Rep,) will be subject to health screening upon arrival.

8. Nationals of Iran, Italy and Korea (Rep.) are not allowed to enter.

9. Passengers who have been in Iran, Italy or Korea (Rep.) in the past 14 days are not allowed to enter Malaysia.

- This does not apply to nationals of Malaysia.

- This does not apply to Malaysian permanent residents, Malaysian social pass holders and Malaysian student passes holders.

Great to see that someone post accurate info. Thanks