Cost would be the hurdle...no Government would be interested in...

Cost would be the hurdle...no Government would be interested in paying for additional screening costs that would do nothing for them.

That said, my Brother in Law went back to Singapore a few weeks ago, he was required to pay $200.00 SGD up front before he left Australia to pay for his covid test when he landed in Singapore.
He was allowed to go to his home where he was notified about 6 hours later that the test was negative. If it were positive he would have been required to wear a bracelet and quarantine at home for 14 days.
The GPS based bracelet alerts health authorities if the wearer leaves their premises...they call the wearer immediately on their nominated phone number if the alert is activated. No answer then you will be paid a visit...no excuses accepted. Straight off to Hotel quarantine under guard.

It seems we taxpayers are paying for all and sundry's covid testing of arrivals in this country...it should be mandated that all intended travelers pay for their test before they leave the port....and are tested on arrival.