More pandering to his base, most things are already shut down in terms of incoming flights.

Pretty much the only ones who can get in are USC and permanent residents.

Even the visa centers outside of the US were already long closed by the time he made this assouncement.

It's just a show announcement, the real action already happened. This maybe just formalizes things. In any case its a good idea on multiple ends of the stick.

Prevents the Covid-19 virus from coming in via foreigners increasing our already epic problems of this fine nation.
Decreases how many arrive at a time of record breaking unemployment.
Even refugees are being told to stay home and they normally get to come in.

He is allowed to cut off immigration for health reasons, but he can also fulfill his racist xenophobic goals of closing down migration to the brown and the yellow.

Trump is not someone to ignore this type of deal. He is a businessman after all, a failed one, but still technically one.

Complimentary Shrek: